Python - logical evaluation order in “if” statement

Question

In Python we can do this:

if True or blah:
    print(\"it\'s ok\") # will be executed

if blah or True: # will raise a NameError
    print(\"it\'s not ok\")
         


        

Answer 1

It's the way the operators logical operators, specifically or in python work: short circuit evaluation.

To better explain it, consider the following:

if True or False:
    print('True') # never reaches the evaluation of False, because it sees True first.

if False or True:
    print('True') # print's True, but it reaches the evaluation of True after False has been evaluated.

For more information see the following:

• The official python documentation on boolean operations
• A stack overflow question regarding short circuitry in python