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<div id="content">
<h1 class="title">The Computer Science Survival Guide - Taming Python</h1>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#orgdc01ab2">Computational Thinking</a>
<ul>
<li><a href="#orge5d8fe5">Step1: Decomposition</a></li>
<li><a href="#orgee76d01">Step2: Pattern Recognition</a></li>
<li><a href="#orge94c4bf">Step3: Abstraction</a></li>
<li><a href="#orgb73d2a6">Step4: Algorithms</a>
<ul>
<li><a href="#orgbea2486">Flowchart Shapes</a></li>
</ul>
</li>
<li><a href="#orgd1bcec8">What is Programming/Coding</a></li>
</ul>
</li>
<li><a href="#org1a8663d">Python</a>
<ul>
<li><a href="#org7413e5b">Syntax</a>
<ul>
<li><a href="#orgdf963bf">Comments</a></li>
<li><a href="#org119eae3">Variables</a></li>
<li><a href="#orgad87821">Operators</a></li>
<li><a href="#org7be2ae6">Data Types</a></li>
<li><a href="#orgcb3be0a">Type Conversion/Casting</a></li>
<li><a href="#org23aa232">Functions</a></li>
<li><a href="#org9c054e7">Defining New Functions</a></li>
<li><a href="#orgacdd1dc">Codeblocks / Indentation</a></li>
<li><a href="#org88c0b37">Syntax Reference Table</a></li>
</ul>
</li>
<li><a href="#org40d6d05">Logic</a>
<ul>
<li><a href="#org438aa1d">Comparison Operators</a></li>
<li><a href="#orge5991db">Boolean Operators</a></li>
<li><a href="#org30f9c3f">IF Statement</a></li>
<li><a href="#org7a72ef4">Loops</a></li>
<li><a href="#org3aaa478">Nested Logic</a></li>
</ul>
</li>
<li><a href="#org593e2f5">Data Structures</a>
<ul>
<li><a href="#orgf1897f5">Sequence Data Structures</a></li>
</ul>
</li>
<li><a href="#org3f5468e">File I/O</a>
<ul>
<li><a href="#org90efa43">Read</a></li>
<li><a href="#org03e7fa3">Write</a></li>
<li><a href="#org5824086">Append</a></li>
<li><a href="#orgbb6a6a7">Parsing</a></li>
</ul>
</li>
<li><a href="#org72f8054">SQL</a></li>
<li><a href="#org1d0bfa3">Handling Errors</a>
<ul>
<li><a href="#org8e24ef9">Syntax Errors</a></li>
<li><a href="#org6c5c240">Logic Error</a></li>
<li><a href="#org8f938d3">Run Time Error</a></li>
<li><a href="#org78ce5d7">Input Validation</a></li>
<li><a href="#orgcad9e08">Debugging</a></li>
<li><a href="#org3a38216">Maintainability / Robustness</a></li>
</ul>
</li>
<li><a href="#orgd3827ea">Advanced</a>
<ul>
<li><a href="#org3fdc911">OOP in Python</a></li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</div>

<div id="outline-container-orgdc01ab2" class="outline-2">
<h2 id="orgdc01ab2">Computational Thinking</h2>
<div class="outline-text-2" id="text-orgdc01ab2">
<div class="keyword">
<p>
Computational thinking is the skill of converting a complex problem into many simple, solvable solutions.
</p>

</div>
<ul class="org-ul">
<li>Thinking computationally is not programming!</li>
<li>The answer a computer can provide is only as good as the question that is first asked of it.</li>
</ul>
</div>

<div id="outline-container-orge5d8fe5" class="outline-3">
<h3 id="orge5d8fe5">Step1: Decomposition</h3>
<div class="outline-text-3" id="text-orge5d8fe5">
<ul class="org-ul">
<li>Firstly take the complex problem and break it down into finite states or actions.</li>
<li>Then take each of these individual smaller problems and check that they can not be broken down further.</li>
</ul>


<div id="org03a8343" class="figure">
<p><object type="image/svg+xml" data="img/decomposition.svg" class="org-svg" width="70%">
Sorry, your browser does not support SVG.</object>
</p>
<p><span class="figure-number">Figure 1: </span>For example consider a vending machine (a complex problem)</p>
</div>
</div>
</div>

<div id="outline-container-orgee76d01" class="outline-3">
<h3 id="orgee76d01">Step2: Pattern Recognition</h3>
<div class="outline-text-3" id="text-orgee76d01">
<p>
Once we have decomposed complex problems we often find  find patterns among the smaller problems we create. 
The patterns are similarities or characteristics that some of the problems share.   
</p>

<p>
We look for:
</p>
<ul class="org-ul">
<li>Problems that repeat/loop</li>
<li>Objects that have similar characteristics</li>
</ul>

<p>
Referring back to the vending machine example:
</p>
<ul class="org-ul">
<li>inserting the money and displaying a balance would likely loop.</li>
<li>items for sale in the vending machine would likely have a cost and description but others be treated similarly.</li>
</ul>

<p>
Finding these patterns allows us to better abstract like elements from the complex problem and solve it more efficiently.  
</p>
</div>
</div>

<div id="outline-container-orge94c4bf" class="outline-3">
<h3 id="orge94c4bf">Step3: Abstraction</h3>
<div class="outline-text-3" id="text-orge94c4bf">
<p>
For each individual problem note the important details outline the entities (nouns) and their actions (verbs), ignore information not absolutely essential to the problem.
</p>

<p>
The vending machine abstracted
</p>
<ul class="org-ul">
<li>the user inserts &lt;inputs&gt; currency</li>
<li>the user makes &lt;inputs&gt; a selection from a menu or a refund</li>
<li>the machine [processes] if the user can afford the selected item</li>
<li>the machine calculates [processes] the change</li>
<li>the machine &lt;outputs&gt; the paid item and change</li>
</ul>
</div>
</div>

<div id="outline-container-orgb73d2a6" class="outline-3">
<h3 id="orgb73d2a6">Step4: Algorithms</h3>
<div class="outline-text-3" id="text-orgb73d2a6">
<div class="keyword">
<p>
An algorithm is a simple set of steps to solve a problem.
</p>

</div>

<ul class="org-ul">
<li>Algorithims are the final result of computational thinking.</li>
<li>For each of the individual problems provide simple step by step solutions.</li>
</ul>

<p>
Almost all problems simplify into three stages: 
</p>
<ul class="org-ul">
<li>Input   : enter values/entities (nouns)</li>
<li>Process : do a calculation or decision (verbs)</li>
<li>Output  : print answer to the screen/file (nouns)</li>
</ul>


<div id="org4ca481c" class="figure">
<p><object type="image/svg+xml" data="img/algorithim.svg" class="org-svg" width="80%">
Sorry, your browser does not support SVG.</object>
</p>
<p><span class="figure-number">Figure 2: </span>Algorithms are written as pseudocode and flowcharts.</p>
</div>
</div>

<div id="outline-container-orgbea2486" class="outline-4">
<h4 id="orgbea2486">Flowchart Shapes</h4>
<div class="outline-text-4" id="text-orgbea2486">

<div id="orgb755cc7" class="figure">
<p><img src="img/REPLACEME.png" alt="REPLACEME.png" width="80%" />
</p>
<p><span class="figure-number">Figure 3: </span>Flowchart Shapes.</p>
</div>
</div>
</div>
</div>

<div id="outline-container-orgd1bcec8" class="outline-3">
<h3 id="orgd1bcec8">What is Programming/Coding</h3>
<div class="outline-text-3" id="text-orgd1bcec8">
<ul class="org-ul">
<li>Programming or coding is the process of entering the steps of an algorithim (instructions) into a computer.</li>
<li>To run an algorithim on a computer it needs to be coded into very explicit binary instructions like 11100110.</li>
<li>Fortunately we no longer program computers directly in binary but use a simpler (higher) programming language like python.</li>
</ul>
</div>
</div>
</div>

<div id="outline-container-org1a8663d" class="outline-2">
<h2 id="org1a8663d">Python</h2>
<div class="outline-text-2" id="text-org1a8663d">
<ul class="org-ul">
<li>Python is a high level English like programming language</li>
<li>look at the following python example :</li>
</ul>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"hello world"</span><span style="color: #4f97d7;">)</span>
</pre>
</div>

<ul class="org-ul">
<li>When the Python code above is run/executed it is interpreted one line at a time into bytecode instructions that the computer can understand.</li>
</ul>
</div>

<div id="outline-container-org7413e5b" class="outline-3">
<h3 id="org7413e5b">Syntax</h3>
<div class="outline-text-3" id="text-org7413e5b">
<p>
Computer Languages such as Python have rules just like human Languages. For example in English a sentence starts with a capital letter and ends in a full stop.
</p>

<div class="keyword">
<p>
Syntax: The rules of a language
</p>

</div>

<p>
Breaking the rules of any language for example incorrect spelling, punctuation or grammar renders it incomprehensible.
</p>
<ul class="org-ul">
<li>Python is no exception and will fail to interpret/understand the code you have entered.</li>
<li>When python is unable to understand your code it will do its best to highlight the <a href="#org8e24ef9">Syntax Errors</a>.</li>
</ul>
</div>

<div id="outline-container-orgdf963bf" class="outline-4">
<h4 id="orgdf963bf">Comments</h4>
<div class="outline-text-4" id="text-orgdf963bf">
<p>
Comments are notes added to code to remind programmers what a piece of code does.
In python a hash character # will begin a comment that extends to the end of the line.
</p>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">this is a comment ignored by the interpreter</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"this is code"</span><span style="color: #4f97d7;">)</span>  <span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">this is also a comment</span>
</pre>
</div>

<div class="keyword">
<p>
Comments are notes for humans ignored by the interpreter
</p>

</div>

<div class="note">
<p>
Comments: Always begin with a #
</p>

</div>
</div>
</div>

<div id="outline-container-org119eae3" class="outline-4">
<h4 id="org119eae3">Variables</h4>
<div class="outline-text-4" id="text-org119eae3">
<p>
Variables are a way of labelling data that is going to be used in a our code.
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">name</span> = <span style="color: #2d9574;">"Mr Kelly"</span>
</pre>
</div>

<div class="keyword">
<p>
A variable is a named value that can be changed
</p>

</div>

<div class="note">
<ul class="org-ul">
<li>Variable names should always relate to the data they hold</li>
<li>Variable names can’t start with a number or contain spaces (use under_scores or CamelCase instead).</li>
</ul>

</div>

<div class="note">
<p>
Variables = are always set after they are named
</p>

</div>
</div>
</div>

<div id="outline-container-orgad87821" class="outline-4">
<h4 id="orgad87821">Operators</h4>
<div class="outline-text-4" id="text-orgad87821">
<p>
Operators are symbols that change the value of a variable :
</p>

<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Symbol</th>
<th scope="col" class="org-left">Operation</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">=</td>
<td class="org-left">Assign the variable on the left the value of the right</td>
</tr>

<tr>
<td class="org-left">+</td>
<td class="org-left">add</td>
</tr>

<tr>
<td class="org-left">-</td>
<td class="org-left">subtract</td>
</tr>

<tr>
<td class="org-left">*</td>
<td class="org-left">multiply</td>
</tr>

<tr>
<td class="org-left">&#47; </td>
<td class="org-left">divide</td>
</tr>

<tr>
<td class="org-left">//</td>
<td class="org-left">integer division</td>
</tr>

<tr>
<td class="org-left">%</td>
<td class="org-left">Modulus</td>
</tr>
</tbody>
</table>


<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This code sets the variable answer to the value of variable1 plus 2</span>
<span style="color: #7590db;">answer</span> = variable1 + <span style="color: #a45bad;">2</span>
</pre>
</div>
</div>
</div>

<div id="outline-container-org7be2ae6" class="outline-4">
<h4 id="org7be2ae6">Data Types</h4>
<div class="outline-text-4" id="text-org7be2ae6">
<p>
A data type describes how data within a variable is stored.
</p>
<ul class="org-ul">
<li>A python variable can store the following types :</li>
</ul>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />

<col  class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Type</th>
<th scope="col" class="org-left">Definition</th>
<th scope="col" class="org-left">Literal</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">integer</td>
<td class="org-left">Whole Number</td>
<td class="org-left">1</td>
</tr>

<tr>
<td class="org-left">float</td>
<td class="org-left">Decimal Number</td>
<td class="org-left">1.0</td>
</tr>

<tr>
<td class="org-left">boolean</td>
<td class="org-left">A value that can only be TRUE or FALSE</td>
<td class="org-left">True or False</td>
</tr>

<tr>
<td class="org-left">string</td>
<td class="org-left">Strings are variables that hold "Text"</td>
<td class="org-left">"Text"</td>
</tr>
</tbody>
</table>


<div class="note">
<p>
"String": Literals are always inside "quotes"
to tell the computer that this is 
"TEXT" not code like
print()
</p>

</div>
</div>
</div>

<div id="outline-container-orgcb3be0a" class="outline-4">
<h4 id="orgcb3be0a">Type Conversion/Casting</h4>
<div class="outline-text-4" id="text-orgcb3be0a">
<p>
When using operators we frequently need to cast variables into compatible types.
</p>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This code has a Type Error </span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">python can't add strings(text) and intergers(numbers) together.</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span> <span style="color: #a45bad;">99</span> + <span style="color: #2d9574;">" Years old"</span> <span style="color: #4f97d7;">)</span> 
<span style="color: #7590db;">answer</span> = <span style="color: #4f97d7;">input</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Please enter a number : "</span> <span style="color: #4f97d7;">)</span> + <span style="color: #a45bad;">1</span> 
</pre>
</div>

<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />

<col  class="org-right" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Function</th>
<th scope="col" class="org-left">Conversion</th>
<th scope="col" class="org-right">Output</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">float(“99”)</td>
<td class="org-left">string -&gt; float</td>
<td class="org-right">99.0</td>
</tr>

<tr>
<td class="org-left">int(“99”)</td>
<td class="org-left">string -&gt; integer</td>
<td class="org-right">99</td>
</tr>

<tr>
<td class="org-left">str(99)</td>
<td class="org-left">number -&gt; string</td>
<td class="org-right">“99”</td>
</tr>
</tbody>
</table>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">However Python can add strings(text) with strings(text)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span> <span style="color: #4f97d7;">str</span><span style="color: #bc6ec5;">(</span><span style="color: #a45bad;">99</span><span style="color: #bc6ec5;">)</span> + <span style="color: #2d9574;">" Years old"</span> <span style="color: #4f97d7;">)</span> 

<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">Python can also add intergers(numbers) with intergers(numbers) </span>
<span style="color: #7590db;">answer</span> = <span style="color: #4f97d7;">int</span><span style="color: #4f97d7;">(</span> <span style="color: #4f97d7;">input</span><span style="color: #bc6ec5;">(</span> <span style="color: #2d9574;">"Please enter a number : "</span> <span style="color: #bc6ec5;">)</span> <span style="color: #4f97d7;">)</span> + <span style="color: #a45bad;">1</span> 
</pre>
</div>
</div>
</div>


<div id="outline-container-org23aa232" class="outline-4">
<h4 id="org23aa232">Functions</h4>
<div class="outline-text-4" id="text-org23aa232">

<div id="org3ee6601" class="figure">
<p><object type="image/svg+xml" data="img/Function.svg" class="org-svg" width="70%">
Sorry, your browser does not support SVG.</object>
</p>
<p><span class="figure-number">Figure 4: </span>Function</p>
</div>

<p>
Functions are a way of reusing sets of instructions that perform the same task.
</p>
<ul class="org-ul">
<li>For example two common functions used in python are print and input:</li>
</ul>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">name</span> = <span style="color: #4f97d7;">input</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Please enter your name : "</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"hello "</span>, name<span style="color: #4f97d7;">)</span>
</pre>
</div>
<ul class="org-ul">
<li>input( "Question ?" )
<ul class="org-ul">
<li>Takes a string to display</li>
<li>captures the users keystrokes until the enter key is pressed</li>
<li>then returns what the user has typed</li>
</ul></li>

<li>print( "OUTPUT" )
<ul class="org-ul">
<li>takes a "string" and displays it on the screen</li>
</ul></li>
</ul>

<div class="keyword">
<p>
Functions are named commands() that may take inputs and/or return an output
</p>

</div>

<div class="note">
<p>
Note Functions always have brackets() after their names 
</p>

</div>
</div>
</div>

<div id="outline-container-org9c054e7" class="outline-4">
<h4 id="org9c054e7">Defining New Functions</h4>
<div class="outline-text-4" id="text-org9c054e7">
<p>
You can also define your own functions using the syntax below:
</p>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">function_name</span><span style="color: #4f97d7;">(</span>input_variable1,input_variable2<span style="color: #4f97d7;">)</span>:
    <span style="color: #2aa1ae;">""" Comment describing what the function does """</span>
    CODEBLOCK
    CODEBLOCK
    CODEBLOCK
    <span style="color: #4f97d7; font-weight: bold;">return</span> output_variable
</pre>
</div>

<div class="note">
<p>
Whenever you reuse your code it should be in a function&#x2026;
</p>

</div>

<div class="note">
<p>
note the use of : to start an indented codeblock
</p>

</div>
</div>
</div>
<div id="outline-container-orgacdd1dc" class="outline-4">
<h4 id="orgacdd1dc">Codeblocks / Indentation</h4>
<div class="outline-text-4" id="text-orgacdd1dc">
<p>
The purpose of a code block is to define statements that will be executed together.
Codeblocks are needed when code forks, loops or is otherwise referenced or reused.
</p>

<p>
In many high level languages instructions can be grouped together into blocks using curly brackets {&#x2026;}.
</p>
<div class="org-src-container">
<pre class="src src-c++"><span style="color: #ce537a; font-weight: bold;">int</span> <span style="color: #bc6ec5; font-weight: bold;">add</span><span style="color: #4f97d7;">(</span><span style="color: #ce537a; font-weight: bold;">int</span> <span style="color: #7590db;">x</span>, <span style="color: #ce537a; font-weight: bold;">int</span> <span style="color: #7590db;">y</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7;">{</span> <span style="color: #2aa1ae; background-color: #292e34;">// </span><span style="color: #2aa1ae; background-color: #292e34;">start a block</span>
    <span style="color: #4f97d7; font-weight: bold;">return</span> x + y;
<span style="color: #4f97d7;">}</span> <span style="color: #2aa1ae; background-color: #292e34;">// </span><span style="color: #2aa1ae; background-color: #292e34;">end a block</span>
</pre>
</div>
<p>
Python separates code-blocks purely on indentation alone as follows :
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">add</span><span style="color: #4f97d7;">(</span>x,y<span style="color: #4f97d7;">)</span>:
    <span style="color: #2aa1ae;">""" As the following lines are indented they belong to the add function """</span>
    <span style="color: #7590db;">Ans</span> = x + y
    <span style="color: #4f97d7; font-weight: bold;">return</span> Ans
</pre>
</div>
</div>
</div>


<div id="outline-container-org88c0b37" class="outline-4">
<h4 id="org88c0b37">Syntax Reference Table</h4>
<div class="outline-text-4" id="text-org88c0b37">
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Syntax Table</th>
<th scope="col" class="org-left">&#xa0;</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left"># Comment</td>
<td class="org-left">Text for humans ignored by the computer</td>
</tr>

<tr>
<td class="org-left">Variable =</td>
<td class="org-left">A named value that can be changed</td>
</tr>

<tr>
<td class="org-left">“String”</td>
<td class="org-left">A variable that holds "Text"</td>
</tr>

<tr>
<td class="org-left">Function( inputs )</td>
<td class="org-left">A named command() that may take inputs and/or return an output</td>
</tr>

<tr>
<td class="org-left">Operators</td>
<td class="org-left">+ plus   - minus   * times   / divide   = assign</td>
</tr>
</tbody>
</table>
</div>
</div>
</div>


<div id="outline-container-org40d6d05" class="outline-3">
<h3 id="org40d6d05">Logic</h3>
<div class="outline-text-3" id="text-org40d6d05">
<p>
Logic statements allow the programmer to control the flow of a program to repeat or execute codeblocks selectively.
</p>
</div>

<div id="outline-container-org438aa1d" class="outline-4">
<h4 id="org438aa1d">Comparison Operators</h4>
<div class="outline-text-4" id="text-org438aa1d">
<p>
Frequently an algorithm needs to compare values (variables) in order make a decision. 
</p>

<div class="note">
<p>
Note the result of a comparison operation is always a boolean ( True or False ).
</p>

</div>

<p>
Python has the following operators to compare variables :
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Symbol</th>
<th scope="col" class="org-left">Operation</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">==</td>
<td class="org-left">Is equal too</td>
</tr>

<tr>
<td class="org-left">!=</td>
<td class="org-left">Is not equal too</td>
</tr>

<tr>
<td class="org-left">&lt;</td>
<td class="org-left">Less than</td>
</tr>

<tr>
<td class="org-left">&lt;=</td>
<td class="org-left">Less than or equal too</td>
</tr>

<tr>
<td class="org-left">&gt;</td>
<td class="org-left">Greater than</td>
</tr>

<tr>
<td class="org-left">&gt;=</td>
<td class="org-left">Greater than or equal too</td>
</tr>
</tbody>
</table>


<div class="note">
<p>
Note the double == means test if the left is equal to the right.
</p>

</div>

<div class="note">
<p>
Be careful with the use of  &gt; GREATER THAN and  &lt; LESS THAN it is very easy to mix them up.
</p>

</div>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">1</span>==<span style="color: #a45bad;">1</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">1</span>!=<span style="color: #a45bad;">2</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">1</span>&lt;<span style="color: #a45bad;">2</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">1</span>&gt;<span style="color: #a45bad;">2</span><span style="color: #4f97d7;">)</span>
</pre>
</div>
</div>
</div>


<div id="outline-container-orge5991db" class="outline-4">
<h4 id="orge5991db">Boolean Operators</h4>
<div class="outline-text-4" id="text-orge5991db">
<p>
For many algorithms logic conditions/statements need to be combined. 
</p>

<p>
Python provides the following boolean operators:
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Symbol</th>
<th scope="col" class="org-left">Operation</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">and</td>
<td class="org-left">TRUE and FALSE = FALSE</td>
</tr>

<tr>
<td class="org-left">or</td>
<td class="org-left">TRUE or  FALSE = TRUE</td>
</tr>

<tr>
<td class="org-left">not</td>
<td class="org-left">Inverts Statement Logic</td>
</tr>
</tbody>
</table>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">True</span> <span style="color: #4f97d7; font-weight: bold;">and</span> <span style="color: #a45bad;">True</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">True</span> <span style="color: #4f97d7; font-weight: bold;">and</span> <span style="color: #a45bad;">True</span> <span style="color: #4f97d7; font-weight: bold;">and</span> <span style="color: #a45bad;">False</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">True</span> <span style="color: #4f97d7; font-weight: bold;">or</span> <span style="color: #a45bad;">False</span> <span style="color: #4f97d7; font-weight: bold;">or</span> <span style="color: #a45bad;">False</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #4f97d7; font-weight: bold;">not</span> <span style="color: #a45bad;">True</span><span style="color: #4f97d7;">)</span>
</pre>
</div>

<div class="note">
<ul class="org-ul">
<li>A single False in a boolean AND statement equates to False.</li>
<li>A single True in a boolean OR statement equates to True.</li>
</ul>

</div>
</div>
</div>


<div id="outline-container-org30f9c3f" class="outline-4">
<h4 id="org30f9c3f">IF Statement</h4>
<div class="outline-text-4" id="text-org30f9c3f">
<div class="keyword">
<p>
IF : Selectively run a codeblock only if a condition is meet (True).
</p>

</div>


<div id="org0c09ee5" class="figure">
<p><object type="image/svg+xml" data="img/if.svg" class="org-svg" width="80%">
Sorry, your browser does not support SVG.</object>
</p>
<p><span class="figure-number">Figure 5: </span>if, else if (elif) and else</p>
</div>


<p>
For example :
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">score</span> = <span style="color: #a45bad;">42</span>
<span style="color: #4f97d7; font-weight: bold;">if</span> score &gt; <span style="color: #a45bad;">80</span>:
    <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Excellent"</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">elif</span> score &gt;= <span style="color: #a45bad;">50</span>
    <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Well Done"</span><span style="color: #4f97d7;">)</span>
<span style="color: #4f97d7; font-weight: bold;">else</span>:
    <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Please Try Again"</span><span style="color: #4f97d7;">)</span>
</pre>
</div>
</div>
</div>

<div id="outline-container-org7a72ef4" class="outline-4">
<h4 id="org7a72ef4">Loops</h4>
<div class="outline-text-4" id="text-org7a72ef4">
<p>
Loops allow us to repeat code according to a condition. Ie:
</p>


<div id="orgb2d79ec" class="figure">
<p><object type="image/svg+xml" data="img/loops.svg" class="org-svg" width="50%">
Sorry, your browser does not support SVG.</object>
</p>
<p><span class="figure-number">Figure 6: </span>Loops</p>
</div>

<ul class="org-ul">
<li>Open umbrella while it is raining</li>

<li>For each student in classroom give candy</li>

<li>Repeat this instruction 10 times</li>
</ul>
</div>

<ul class="org-ul"><li><a id="org7d47559"></a>While Loop<br /><div class="outline-text-5" id="text-org7d47559">
<div class="keyword">
<p>
While: A statement that repeats a codeblock while the condition is True.
</p>

</div>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">weather</span> = <span style="color: #2d9574;">"Raining"</span>

<span style="color: #4f97d7; font-weight: bold;">while</span> weather == <span style="color: #2d9574;">"Raining"</span>:
    <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"It is raining, umbrella open"</span><span style="color: #4f97d7;">)</span>

<span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"It is no longer raining close umbrella"</span><span style="color: #4f97d7;">)</span>
</pre>
</div>

<p>
note the above will create an <a href="#org1b4eba4">infinite loop</a> as weather always == "Raining" 
</p>
</div></li>

<li><a id="org258f4b7"></a>For Loop<br /><div class="outline-text-5" id="text-org258f4b7">
<div class="keyword">
<p>
For : A statement that repeats a codeblock a known number of times. 
</p>

</div>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">The range statement controls the for loops begining termination and step</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">the for loop below begins at 1 terminates at 11 and steps by 1 each loop </span>
<span style="color: #4f97d7; font-weight: bold;">for</span> i <span style="color: #4f97d7; font-weight: bold;">in</span> <span style="color: #4f97d7;">range</span><span style="color: #4f97d7;">(</span><span style="color: #a45bad;">1</span>,<span style="color: #a45bad;">11</span>,<span style="color: #a45bad;">1</span><span style="color: #4f97d7;">)</span>:
    <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span>i<span style="color: #4f97d7;">)</span>
</pre>
</div>

<div class="note">
<p>
For loops do not execute their terminal iteration; That is the loop above will print 1..10 not 11   
</p>

</div>
</div></li>

<li><a id="orge385ef6"></a>Recursive Functions<br /><div class="outline-text-5" id="text-orge385ef6">
<p>
Another easy way to loop based on the outcome of a previous calculation/input is to recursively call a function.
</p>

<p>
For example <a href="#org78ce5d7">validating user input</a> by asking them to repeat an input that couldn't be understood :
</p>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">input_int_min_max</span><span style="color: #4f97d7;">(</span>prompt,MIN, MAX<span style="color: #4f97d7;">)</span>:
    <span style="color: #2aa1ae;">""" Simplified Validation Function to ensure the user enters an integer between min and max"""</span>
    <span style="color: #4f97d7; font-weight: bold;">if</span><span style="color: #4f97d7;">(</span>num &gt;= MIN <span style="color: #4f97d7; font-weight: bold;">and</span> num &lt;= MAX<span style="color: #4f97d7;">)</span>:
        <span style="color: #4f97d7; font-weight: bold;">return</span> num
    <span style="color: #4f97d7; font-weight: bold;">else</span>:
        <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"INVAILD"</span><span style="color: #4f97d7;">)</span>
        <span style="color: #4f97d7; font-weight: bold;">return</span> input_int_min_max<span style="color: #4f97d7;">(</span>prompt,MIN, MAX<span style="color: #4f97d7;">)</span>
</pre>
</div>

<div class="keyword">
<p>
Recursive Function : A function that calls itself directly or indirectly forming a loop
</p>

</div>
</div></li></ul>
</div>


<div id="outline-container-org3aaa478" class="outline-4">
<h4 id="org3aaa478">Nested Logic</h4>
<div class="outline-text-4" id="text-org3aaa478">
<p>
For complex problems it is also possible to nest logic statements within each other.
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">if</span> weather == <span style="color: #2d9574;">"Wet"</span>:
    <span style="color: #4f97d7; font-weight: bold;">if</span> weather == <span style="color: #2d9574;">"Windy"</span>:
        <span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">wet and windy</span>
        <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Take Raincoat"</span><span style="color: #4f97d7;">)</span>
    <span style="color: #4f97d7; font-weight: bold;">else</span>:
        <span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">just wet</span>
        <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Take Umbrella"</span><span style="color: #4f97d7;">)</span>
</pre>
</div>
<p>
Avoid nesting your code if possible as it makes code more difficult to read and debug, common solutions include:
</p>

<p>
simplifying boolean statements, for example :
</p>

<p>
use functions for duplicate fork code : 
</p>
</div>
</div>
</div>

<div id="outline-container-org593e2f5" class="outline-3">
<h3 id="org593e2f5">Data Structures</h3>
<div class="outline-text-3" id="text-org593e2f5">
<div class="keyword">
<p>
Data structures are a way to organise related data together with methods to access and manipulate them efficiently.
</p>

</div>
<p>
Often a program needs to work with many similar variables such as items, names, groups etc.
Consider for example a simple program that averages the scores for 30 students:
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">student_score1</span> = <span style="color: #a45bad;">10</span>
<span style="color: #7590db;">student_score2</span> = <span style="color: #a45bad;">20</span>
<span style="color: #7590db;">student_score3</span> = <span style="color: #a45bad;">30</span>
...
<span style="color: #7590db;">total</span> = student_score1 + student_score2 + ... 
<span style="color: #7590db;">average</span> = total / <span style="color: #a45bad;">30</span>
</pre>
</div>
<p>
Although the above would solve the average, it has limitations:
</p>
<ul class="org-ul">
<li>The code above will only work for exactly 30 students.</li>
<li>Coding without data containers would be more time consuming rewriting very similar instructions.</li>
<li>The programmer is very likely to make mistakes.</li>
</ul>
</div>


<div id="outline-container-orgf1897f5" class="outline-4">
<h4 id="orgf1897f5">Sequence Data Structures</h4>
<div class="outline-text-4" id="text-orgf1897f5">
<p>
Python sequences (strings, lists tuples) are ordered data structures that allow a single identifier to index more than one value.
</p>


<div id="org74adc7e" class="figure">
<p><object type="image/svg+xml" data="img/array.svg" class="org-svg" width="50%">
Sorry, your browser does not support SVG.</object>
</p>
<p><span class="figure-number">Figure 7: </span>Sequence of length 4</p>
</div>
</div>

<ul class="org-ul"><li><a id="org8d4b1f0"></a>Python Strings<br /><div class="outline-text-5" id="text-org8d4b1f0">
<p>
A string is specialized data structure to hold a sequence of characters.
A character is simply a symbol such as the letters of the English language (Python, string is a sequence of Unicode encoded characters) . 
</p>

<div class="note">
<p>
Note unlike other languages python :
</p>
<ul class="org-ul">
<li>doesen't have a char type, just a string of a single char</li>
<li>strings are immutable, can not be edited</li>
</ul>

</div>

<p>
Updating Strings
You can "update" an existing string by (re)assigning a variable to another string.
</p>
</div></li>

<li><a id="org6f514b9"></a>Python Lists and Tuples<br /><div class="outline-text-5" id="text-org6f514b9">
<p>
Unlike strings that contain only characters, list and tuples can contain any type of objects
</p>

<p>
The previous averaging problem can be solved using a list data structure:
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">sum : total the values of each item in the list</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">len : count the number of values held in the list</span>
<span style="color: #7590db;">listValues</span> = <span style="color: #4f97d7;">[</span><span style="color: #a45bad;">10</span>,<span style="color: #a45bad;">20</span>,<span style="color: #a45bad;">30</span>,<span style="color: #a45bad;">40</span><span style="color: #4f97d7;">]</span>
<span style="color: #7590db;">average</span> = <span style="color: #4f97d7;">sum</span><span style="color: #4f97d7;">(</span>listValues<span style="color: #4f97d7;">)</span> / <span style="color: #4f97d7;">len</span><span style="color: #4f97d7;">(</span>listValues<span style="color: #4f97d7;">)</span>
</pre>
</div>
<ul class="org-ul">
<li>This solution will work for any number of students and is much easier and less error prone for the programmer.</li>
</ul>

<div class="note">
<ul class="org-ul">
<li>Note unlike other language python uses link lists for its data structures (most languages use congruent and adjacent arrays).</li>
<li>As Python is dynamicly typed Language items in a list need not be of the same type.</li>
</ul>

</div>


<p>
List deletion
</p>
</div>

<ul class="org-ul"><li><a id="org2e29778"></a>Nested lists<br /></li>


<li><a id="orgd275937"></a>Strings and lists<br /></li></ul></li></ul>
</div>
</div>


<div id="outline-container-org3f5468e" class="outline-3">
<h3 id="org3f5468e">File I/O</h3>
<div class="outline-text-3" id="text-org3f5468e">
<p>
binary and text &#x2026;
</p>
</div>

<div id="outline-container-org90efa43" class="outline-4">
<h4 id="org90efa43">Read</h4>
</div>
<div id="outline-container-org03e7fa3" class="outline-4">
<h4 id="org03e7fa3">Write</h4>
</div>
<div id="outline-container-org5824086" class="outline-4">
<h4 id="org5824086">Append</h4>
</div>

<div id="outline-container-orgbb6a6a7" class="outline-4">
<h4 id="orgbb6a6a7">Parsing</h4>
</div>
</div>


<div id="outline-container-org72f8054" class="outline-3">
<h3 id="org72f8054">SQL</h3>
<div class="outline-text-3" id="text-org72f8054">
<p>
Server Query Language &#x2026; really is a book worthy topic 
CRUD
</p>
</div>
</div>

<div id="outline-container-org1d0bfa3" class="outline-3">
<h3 id="org1d0bfa3">Handling Errors</h3>
<div class="outline-text-3" id="text-org1d0bfa3">
<p>
Murphy's law Anything that can go wrong will go wrong
</p>
</div>

<div id="outline-container-org8e24ef9" class="outline-4">
<h4 id="org8e24ef9">Syntax Errors</h4>
<div class="outline-text-4" id="text-org8e24ef9">
<p>
Syntax errors are the result of breaking the rules of the python language such as spelling, punctuation etc.
</p>
<ul class="org-ul">
<li>When python is unable to understand your code it will do its best to highlight the syntax error.</li>
</ul>

<div class="figure">
<p><img src="img/syntax_error.jpg" alt="syntax_error.jpg" />
</p>
</div>
<ul class="org-ul">
<li>The example python code above contains multiple errors.
<ul class="org-ul">
<li>print is misspelt Pr0nt (note python is case sensitive)</li>
<li>the string "Syntax is missing a double quote</li>
<li>the print function is missing a closing bracket</li>
</ul></li>
</ul>

<div class="keyword">
<p>
Syntax Error : The code cannot be interpreted as it violates the rules of the language	 
</p>

</div>
</div>
</div>
<div id="outline-container-org6c5c240" class="outline-4">
<h4 id="org6c5c240">Logic Error</h4>
<div class="outline-text-4" id="text-org6c5c240">
<div class="keyword">
<p>
Logic Error : The code runs but produces the incorrect output for some or all input(s)	 
</p>

</div>
</div>

<ul class="org-ul"><li><a id="org1b4eba4"></a>Infinite Loops<br /><div class="outline-text-5" id="text-org1b4eba4">
<p>
Infinite loops are a type of logic error where by a program loops through a codeblock endlessly.  
There are three common causes of infinite loops:
</p>
<ul class="org-ul">
<li>resetting the conditional variable incorrectly</li>
</ul>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">num</span> = <span style="color: #a45bad;">1</span>
<span style="color: #4f97d7; font-weight: bold;">while</span> num &gt; <span style="color: #a45bad;">0</span>:
    <span style="color: #7590db;">num</span> = <span style="color: #a45bad;">10</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This will loop forever as num is reset within the loop.</span>
</pre>
</div>

<ul class="org-ul">
<li>incorrect comparison operator</li>
</ul>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #7590db;">num</span> = <span style="color: #a45bad;">0</span>
<span style="color: #4f97d7; font-weight: bold;">while</span> num &lt; <span style="color: #a45bad;">0</span>:
    <span style="color: #7590db;">num</span> = num - <span style="color: #a45bad;">1</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This will loop forever as num will always be Less than zero.</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">the programmer either intended to use &gt; Greater than or for num to increment </span>
</pre>
</div>
<ul class="org-ul">
<li>unbreakable condition</li>
</ul>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">while</span> <span style="color: #a45bad;">True</span>:
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This will always loop as the condition is True.</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This loop can only be broken with the use of a Break statement </span>
</pre>
</div>
<p>
alternatively in the case of recursive functions
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">recursive_fun</span><span style="color: #4f97d7;">()</span>:
    <span style="color: #4f97d7; font-weight: bold;">return</span> recursive_fun<span style="color: #4f97d7;">()</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">This function calls itself directly without a breakable condition</span>
<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">Be careful this can also happen indirectly with many functions calling each other.</span>
</pre>
</div>
</div></li></ul>
</div>
<div id="outline-container-org8f938d3" class="outline-4">
<h4 id="org8f938d3">Run Time Error</h4>
<div class="outline-text-4" id="text-org8f938d3">
<div class="keyword">
<p>
Run Time Error : The code fails during execution  	 
</p>

</div>

<p>
Using an undeclared variable or indexing out of range 
</p>
</div>

<ul class="org-ul"><li><a id="orgda91ed7"></a>exception handling<br /><div class="outline-text-5" id="text-orgda91ed7">
<p>
When an error occurs in python it terminates the current instruction and raises an exception.
If the exception isn't handled by the program it is terminated and an error message is output to the shell.
</p>

<p>
Therefore if you have some code that may raise an exception (opening files/networks, user input) 
you should place the code in a try except block.
</p>

<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">try</span>:
  doSomething<span style="color: #4f97d7;">()</span> <span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">that may crash</span>
<span style="color: #4f97d7; font-weight: bold;">except</span>: 
  <span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">doSomething() has caused a crash so</span>
  do_something_else<span style="color: #4f97d7;">()</span>
<span style="color: #4f97d7; font-weight: bold;">else</span>:
  <span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">doSomething() is good so</span>
  save<span style="color: #4f97d7;">()</span>
</pre>
</div>

<p>
The codeblock between the try and except is first executed.
If no exception occurs, the except clause is skipped and the optional else codeblock is executed.
</p>
</div></li></ul>
</div>

<div id="outline-container-org78ce5d7" class="outline-4">
<h4 id="org78ce5d7">Input Validation</h4>
<div class="outline-text-4" id="text-org78ce5d7">
<p>
It is sound programming practice to protect your program from invalid and malicious input.
</p>

<div class="note">
<p>
Accepting invalid input is a cause of run time errors and is also a security concern.
</p>

</div>


<p>
Data type validation :
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">input_int</span><span style="color: #4f97d7;">()</span>:
    <span style="color: #4f97d7; font-weight: bold;">try</span>:
        <span style="color: #7590db;">number</span> = <span style="color: #4f97d7;">int</span><span style="color: #4f97d7;">(</span><span style="color: #4f97d7;">input</span><span style="color: #bc6ec5;">(</span><span style="color: #2d9574;">"INPUT NUMBER \n : "</span><span style="color: #bc6ec5;">)</span><span style="color: #4f97d7;">)</span>
    <span style="color: #4f97d7; font-weight: bold;">except</span>:
        <span style="color: #4f97d7; font-weight: bold;">print</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"Input Invalid Please enter a whole number in the format 10"</span><span style="color: #4f97d7;">)</span>
        input_int<span style="color: #4f97d7;">()</span>
    <span style="color: #4f97d7; font-weight: bold;">else</span>:
        <span style="color: #4f97d7; font-weight: bold;">return</span> number
</pre>
</div>

<p>
Range validation
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">int_min_max</span><span style="color: #4f97d7;">(</span>num, MIN, MAX<span style="color: #4f97d7;">)</span>:
    <span style="color: #4f97d7; font-weight: bold;">if</span><span style="color: #4f97d7;">(</span>num &gt;= MIN <span style="color: #4f97d7; font-weight: bold;">and</span> num &lt;= MAX<span style="color: #4f97d7;">)</span>:
        <span style="color: #4f97d7; font-weight: bold;">return</span> num
    <span style="color: #4f97d7; font-weight: bold;">else</span>:
        <span style="color: #4f97d7; font-weight: bold;">return</span> <span style="color: #a45bad;">None</span>
</pre>
</div>

<p>
Constraint validation
</p>
<div class="org-src-container">
<pre class="src src-python"><span style="color: #4f97d7; font-weight: bold;">def</span> <span style="color: #bc6ec5; font-weight: bold;">yes_or_no</span><span style="color: #4f97d7;">()</span>:
    <span style="color: #7590db;">user_choice</span> = <span style="color: #2d9574;">""</span>
    <span style="color: #4f97d7; font-weight: bold;">while</span> user_choice <span style="color: #4f97d7; font-weight: bold;">not</span> <span style="color: #4f97d7; font-weight: bold;">in</span> <span style="color: #4f97d7;">[</span><span style="color: #2d9574;">"yes"</span>,<span style="color: #2d9574;">"no"</span><span style="color: #4f97d7;">]</span>:
        <span style="color: #7590db;">user_choice</span> = <span style="color: #4f97d7;">input</span><span style="color: #4f97d7;">(</span><span style="color: #2d9574;">"yes or no"</span><span style="color: #4f97d7;">)</span>.lower<span style="color: #4f97d7;">()</span>  
    <span style="color: #4f97d7; font-weight: bold;">return</span> user_choice   
</pre>
</div>
</div>
</div>
<div id="outline-container-orgcad9e08" class="outline-4">
<h4 id="orgcad9e08">Debugging</h4>
<div class="outline-text-4" id="text-orgcad9e08">
<div class="keyword">
<p>
Debugging: The process of identify and correcting the cause of an error
</p>

</div>

<p>
Although the python interpreter does its best to inform the user as to cause of a crash (such as dividing by zero) in complex programs it is often unclear what the cause of the error was (ie why and where did the program divide by zero).
</p>

<p>
However depending on your IDE (integrated development environment) a python programmer has many tools at their disposal for example <a href="https://www.cs.uky.edu/~keen/help/debug-tutorial/debug.html">idle</a> has its own debugger.
<a href="http://winpdb.org/">http://winpdb.org/</a>
</p>

<p>
This guide will detail the use of Pythons debugger module, pdb.
</p>
</div>

<ul class="org-ul"><li><a id="orgee28487"></a>Tracing<br /><div class="outline-text-5" id="text-orgee28487">
<p>
Tracing is a debugging technique where by a programmer follows the execution of their code line by line. As this can be a tedious process in larger programs, programmers often start a trace at a point of interest in their code rather the beginning.
</p>

<p>
A debugging tool makes this easy to do, by allowing you to execute your program line by line, querying the values of variables along the way.
</p>


<div class="org-src-container">
<pre class="src src-python"><span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">Firslty import the pdb module at the top of your python file</span>
<span style="color: #4f97d7; font-weight: bold;">import</span> pdb

<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">... clean code that we know works ...</span>

<span style="color: #2aa1ae; background-color: #292e34;"># </span><span style="color: #2aa1ae; background-color: #292e34;">Next to begin a trace, insert the following code above the line of interest:</span>
pdb.set_trace<span style="color: #4f97d7;">()</span>

</pre>
</div>

<p>
Python will execute the program as normal until it encounters pdb.set_trace().
Python will then pause execution, display the next line that will be executed and wait for your command.
</p>

<p>
Pdb offers the following commands to inspect the current state of the paused program :
</p>
<table border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">


<colgroup>
<col  class="org-left" />

<col  class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Command</th>
<th scope="col" class="org-left">Operation</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">n</td>
<td class="org-left">Execute the next statement</td>
</tr>

<tr>
<td class="org-left">p var</td>
<td class="org-left">Print the current value of var</td>
</tr>

<tr>
<td class="org-left">l</td>
<td class="org-left">where am I (list current statements)</td>
</tr>

<tr>
<td class="org-left">c</td>
<td class="org-left">stop debugging run normally until next pdb.set_trace()</td>
</tr>

<tr>
<td class="org-left">r</td>
<td class="org-left">stop debugging run normally untilnext return</td>
</tr>

<tr>
<td class="org-left">q</td>
<td class="org-left">quit</td>
</tr>
</tbody>
</table>
</div></li></ul>
</div>

<div id="outline-container-org3a38216" class="outline-4">
<h4 id="org3a38216">Maintainability / Robustness</h4>
<div class="outline-text-4" id="text-org3a38216">
<p>
The following are considered good programming practice and are essential in ensuring that every program is robust and maintainable:  
</p>
<ul class="org-ul">
<li>Coding style and naming convention
<ul class="org-ul">
<li>To the greatest extent possible write code that is Pythonic and literal.</li>
<li>Module,Classes,Functions and Variables all need consistent meaningful names.</li>
<li>(KEEP IT SIMPLE STUPID) good python code reads almost like English.</li>
</ul></li>
<li>Comments 
<ul class="org-ul">
<li>Concise meaningful comments are best, little and often</li>
</ul></li>
<li>Functions
<ul class="org-ul">
<li>If you ever copy and paste code ask yourself should this be a function or a class?</li>
<li>have I simplified/modelled the problem properly ?</li>
</ul></li>
<li>Modules 
<ul class="org-ul">
<li>Don't write absolutely everything into one huge python file, use separate modules for larger projects and reusable components.</li>
</ul></li>
</ul>
</div>
</div>
</div>


<div id="outline-container-orgd3827ea" class="outline-3">
<h3 id="orgd3827ea">Advanced</h3>
<div class="outline-text-3" id="text-orgd3827ea">
</div><div id="outline-container-org3fdc911" class="outline-4">
<h4 id="org3fdc911">OOP in Python</h4>
</div>
</div>
</div>
</div>
</body>
</html>