dynamic_language.md

Dynamic Language

Because python is a dynamic language, there are many things that other languages can't do, and this is also mentioned in the documentation: 9.7. Odds and Ends.

Table of Contents

• Dynamic Language
  • Table of Contents
  • Define class in condition
  • Define class in For-loop
  • Pre-defined in class
  • Post-defined Class variables
  • Post-defined Instance variables

Define class in condition

We can define a class inside a function, and even create a class by using condition (if-else). Of course, you can also create functions by condition.

def getClass(x):
    if x == 1:
        class ClassA:
            x = 1
        return ClassA
    else:
        class ClassB:
            x = 0
        return ClassB
    
cls = getClass(1)
print(cls)    # <class '__main__.getClass.<locals>.ClassA'>
print(cls.x)  # 1

Define class in For-loop

We can also create classes in a loop and keep the last class created when we leave.

for i in range(10):
    class ClassA:
        x = i
        
    cls = ClassA()
    print(cls.x)  # 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

print(cls.x)  # 9

Pre-defined in class

We can define class variables and instance variables in class early, and then use them outside when they are ready.

class Example:
    def hi(self):
        print(Example.cls_var)
        print(self.inst_var)


e = Example()
Example.cls_var = "ya"
e.inst_var = "wow"

e.hi()  # ya, wow

Post-defined Class variables

We can implement class variables after defining class.

class Example:
    pass

Example.cls_a = 1

e = Example()
print(e.cls_a)  # 1

Post-defined Instance variables

We can implement instance variables after defining class.

class Example:
    pass

e = Example()
e.msg = "wow"
e.hi = lambda self: print(self.msg)

e.hi(e)  # wow