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iterators and iterables
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‎P-E-iterators and iterables.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"id": "b3c0145c",
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"metadata": {},
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"source": [
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"# Python: Everything\n",
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"- 25) **Iterators and iterables:** \n",
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"<br>----------------------------------------------\n",
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"<br> https://www.pinterest.com/HamedShahHosseini/programming-languages/\n",
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"<br>https://github.com/ostad-ai/Python-Everything"
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]
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},
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{
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"cell_type": "markdown",
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"id": "35474859",
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"metadata": {},
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"source": [
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"**Iterator:** is an object that allows us to iterate over collections of data. Therefore, the data is traversed or accessed one item at a time by an iterator.\n",
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"<br>An iterator class must implement two special methods **iter** and **next**.\n",
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"<br> **iter** is called to initialize the iterator, and it must return the iterator object.\n",
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"<br> **next** is called to iterate over the iterator, and must return the next value in the given data stream."
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]
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},
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{
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"cell_type": "markdown",
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"id": "68263de5",
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"metadata": {},
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"source": [
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"In contrast, we have iterables, which we can get an iterator from by using the iter() method. it also supports next() method, which returns the next value in the iterable.\n",
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"<br> Lists, sets, tuples, strings, and dictionaries are all iterables."
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]
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},
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{
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"cell_type": "markdown",
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"id": "8d2a1b9c",
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"metadata": {},
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"source": [
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"In the following, we define a list, and see the use of iter() and next() methods"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"id": "a32fc742",
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"hello, world, then, bye, "
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]
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}
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],
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"source": [
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"mylist=['hello','world','then','bye']\n",
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"myiter=iter(mylist)\n",
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"while True:\n",
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" try:\n",
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" print(next(myiter),end=', ')\n",
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" except:\n",
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" break"
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]
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},
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{
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"cell_type": "markdown",
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"id": "e8735221",
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"metadata": {},
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"source": [
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"The easy way to traverse over elements of an iterable is using for-loop"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"id": "221b79d6",
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"hello, world, then, bye, "
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]
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}
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],
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"source": [
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"mylist=['hello','world','then','bye']\n",
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"for el in mylist:\n",
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" print(el,end=', ')"
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]
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},
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{
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"cell_type": "markdown",
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"id": "1d60f725",
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"metadata": {},
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"source": [
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"Let's define an iterator class, which must implement iter() and next() methods.\n",
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"<br> We may have at least three different types of custom iterators:\n",
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"1. Take a data sequence, and return its items, one at a time\n",
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"2. Take a data sequence, transform each item, and return the trasnformed item, one after the other.\n",
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"3. Generate a new sequence of data, and return its items one after the other."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"id": "f0078a85",
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"1, 3, 5, 7, 9, 11, 13, 15, 17, 19, "
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]
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}
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],
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"source": [
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"# a class that generates odd numbers\n",
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"class oddNumbers:\n",
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" def __init__(self,start=1):\n",
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" self._number=start\n",
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" def __iter__(self):\n",
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" return self\n",
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" def __next__(self):\n",
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" item=self._number\n",
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" self._number+=2\n",
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" return item\n",
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"odds=iter(oddNumbers())\n",
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"for i in range(10):\n",
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" print(next(odds),end=', ')"
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]
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},
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{
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"cell_type": "markdown",
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"id": "9f3ea82d",
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"metadata": {},
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"source": [
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"The oodNumbers class runs for ever, so if we use it in a for loop, it never ends. <br> To have a limit on the length of the sequence, we may use **StopIteration** with keyword raise."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"id": "87da7a5d",
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"1, 3, 5, 7, 9, 11, 13, 15, 17, 19, "
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]
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}
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],
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"source": [
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"# a class that generates odd numbers with a limit\n",
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"class oddNumbers2:\n",
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" def __init__(self,start=1,Nelements=10):\n",
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" self._number=start\n",
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" self._length=Nelements\n",
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" self._index=0\n",
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" def __iter__(self):\n",
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" return self\n",
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" def __next__(self):\n",
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" if self._index<self._length:\n",
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" item=self._number\n",
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" self._number+=2\n",
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" self._index+=1\n",
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" return item\n",
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" else:\n",
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" raise StopIteration\n",
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"odds2=oddNumbers2()\n",
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"for odd in odds2:\n",
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" print(odd,end=', ')"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "22275727",
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"metadata": {},
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"outputs": [],
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"source": []
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3 (ipykernel)",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.11.1"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 5
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}

‎README.md

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21) SQLite3 module, introduction: We can use *sqlite3* module in Python for creating and accessing databases without the need to have a separate server. Here, we use basic commands of **SQL** for such purposes. For example, for creating and manipulating tables in our database.
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22) Operator overloading in Python: Using built-in operators, it is possible to change their behaviors via implementing their relevant special methods in a custom class definition. Here, we implement operator == for almost-equal. Also, we implement operator + for vector summation.
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23) Lambda expressions: We may use lambda keyword to define anonymous functions. Here, we define the syntax for lambda expressions, and then we bring some applications.
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24) Magic methods, __getitem__ and __setitem__: We review getitem and setitem methods that may be used for **indexing** and **assignment** on instances of a class, respectively.
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24) Magic methods, __getitem__ and __setitem__: We review getitem and setitem methods that may be used for **indexing** and **assignment** on instances of a class, respectively.
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25) Iterators and iterables: We use iterators to iterate over iterables. This section reviews both of them. Lists, sets, tuples, and dictionaries are examples of iterables.

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