Int is not a keyword, What happens if we use it as a variable?

Question

Int is not a keyword in python, and hence can be used as a variable name. I tried to assign a string into the name and it worked.

I did this in the IDLE of Python3.8.2

>>> a = int(4.5)
>>> print(a)
4
>>> int = 'abc'
>>> print(int)
abc
>>> b = int(5.7)
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    b = int(5.7)
TypeError: 'str' object is not callable
>>> print(b)

the code works without the last part. ie from b = int(5.7)

Why does it happen? and shouldn't int be a keyword? how can we fix it keeping the existing code intact as if working in the console?

I tried using the del keyword and it worked. but I don't know why.

>>> del int
>>> b = int(5.7)
>>> print(b)
5

This works.

Please explain. :)

Answer 1

None of the basic types are keywords, they are type objects

>>> type(int)
<class 'type'>

and they create instances of their class when used

>>> type(int('100'))
<class 'int'>

They work like classes you define yourself

>>> class Foo:
...     pass
... 
>>> type(Foo)
<class 'type'>
>>> type(Foo())
<class '__main__.Foo'>

The only difference is that they are in the "builtins" namespace, but due to python's scoping rule, "builtins" is check last. Any variable you create is in a namespace checked before builtins so shadows the builtin itself.

As for why, just about everything in python is a first class object and they all follow the same rules. There is no special code or any special rules for int (other than its implementation) - it works the same as any other class.

Namespaces are hierarchical, mostly builtins --> module --> local meaning that local shadows module which shadows builtins. del removes a variable from a namespace, removing that shadow. If you create a variable called int and then del int , python will no longer find it in the local namespace and will fall back to the original.

Of course, you can always mess things up on a more permanent basis if you wish:

>>> __builtins__.__dict__['int'] = float
>>> int(1)
1.0