Question

There is this code:

>>> if True:
...     a = 4
... 
>>> print a
4

Why variable a is still alive after if block? Shouldn’t it be destroyed when block if ends?

Answer 1

Python variables have scope inside a function, class or module. Variables initialised in if statements, while statements and for statements are available outside the if/while/for statement for use

This is different to many other languages where accessing the variable would throw an exception because of it being out of scope

Just to note, if the if/while/for statement is false and does not execute, a for example would not be initialised and it would throw an error like so:

>>> if False:
...     a = 5
... 
>>> print a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined