How can I tell if variable is defined

Tue Sep 22 14:35:44 EDT 2009

On 2009年9月22日 11:03:25 -0700, Brown, Rodrick 
<rodrick.brown at citi.com> wrote:
> How could I do the following check in Python
>> In Perl I could do something like if ((defined($a)) { ... }
>> I tried if var is not None:
> However this doesn't seem to work as described.
>> Thanks.

Could you let us know in what context you're checking to see if a variable 
is defined? If you mean "has the name been used before", then bear in mind 
Python is a lot stricter about this kind of thing than Perl, and if you've 
never used 'var' before the if-statement, you'll probably get a NameError 
being raised.
If you want to check whether the name 'var' is bound to a meaningful 
object, however (e.g. if it's an optional argument to a function, and you 
know it exists, but don't know if it's bound to meaningful data) then your 
construction should work.
-- 
Rami Chowdhury
"Never attribute to malice that which can be attributed to stupidity" -- 
Hanlon's Razor
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