Easy way to check that a variable is defined in python? [duplicate]

Answer 1

Read and or tricks in python : 'a' in locals() and a

Answer 2

A compact way:

print myObject.myVar if hasattr(myObject, 'myVar') else 'not defined'

htw's way is more Pythonic, though.

hasattr() is different from x in y.__dict__, though: hasattr() takes inherited class attributes into account, as well as dynamic ones returned from __getattr__, whereas y.__dict__ only contains those objects that are attributes of the y instance.

Answer 3

try:
    print myObject.myVar
except NameError:
    print "not defined"

Answer 4

Paolo is right, there may be something off with the way you're doing things if this is needed. But if you're just doing something quick and dirty you probably don't care about Idiomatic Python anway, then this may be shorter.

try: x
except: print "var doesn't exist"

Answer 5

To test if the variable, myvar, is defined:

result = dir().count('myvar')

If myvar is defined, result is 1, otherwise it would be 0.

This works fine in Python version 3.1.2.