function to check whether a variable already exists?

[Graham Guttocks]

Can anyone tell me how to wrap the following in a function as to
avoid typing this try, except sequence for every variable whose
existence I want to check?

For example,

try:
    if NEWSRC:pass
except NameError:
    NEWSRC = os.path.expanduser("~/.newsrc")

It seems tricky, because you can't just pass a function NEWSRC because
if it doesn't first exist NameError will immediately be raised.

Regards,
Graham

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