# b is first defined inside a trivially true if statement
In [6]: if True:
   ...:     b = 21
   ...:
# b is still defined globally
In [7]: b
Out[7]: 21

# it does matter that the if statement is evaluated
In [10]: if False:
   ....:     b = 1337
   ....:
In [11]: b
Out[11]: 21