Determine if variable is defined in Python

Question

How do you know whether a variable has been set at a particular place in the code at runtime? This is not always obvious because (1) the variable could be conditionally set, and (2) the variable could be conditionally deleted. I'm looking for something like defined() in Perl or isset() in PHP or defined? in Ruby.

if condition:

a = 42

# is "a" defined here?

if other_condition:

del a

# is "a" defined here?

Answer 1

If you want to know whether a variable has been set at a particular place in the code at runtime you can use the following piece of code:-

         

try:

thevariable

except NameError:

print("well, it WASN'T defined after all!")

else:

print("sure, it was defined.")

Answer 2

Try using this:

'a' in vars() or 'a' in globals()

But, if you want to be pedantic, then you can check the builtins too like this:

'a' in vars(__builtins__)