📅  最后修改于: 2022-03-11 14:46:53.498000             🧑  作者: Mango
Testing if a Variable Is Defined
Credit: Hamish Lawson
Problem
You want to take different courses of action based on whether a variable is defined.
Solution
In Python, all variables are expected to be defined before use. The None object is a value you often assign to signify that you have no real value for a variable, as in:
try: x
except NameError: x = None
Then it’s easy to test whether a variable is bound to None:
if x is None:
some_fallback_operation( )
else:
some_operation(x)