How can I tell if variable is defined
Peter Otten
__peter__ at web.de
Tue Sep 22 17:01:50 EDT 2009
Mel wrote:
> Grant Edwards wrote:
>
>> On 2009-09-22, 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)) { ... }
>>
>> try:
>> yourNameHere
>> except NameError:
>> print "undefined"
>> else:
>> print "defined"
>
> This being Python, however, it can be fooled:
>
> Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41)
> [GCC 4.3.3] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> class A():
> ... def __repr__ (self):
> ... global b
Superfluous global statement.
> ... return b
> ...
>>>> a = A()
>>>> try:
> ... a
> ... except NameError:
> ... print "`a` is not defined"
> ...
> `a` is not defined
This is an artifact of the interactive interpreter, like the following way
to print 42:
>>> for i in range(3): 42
...
42
42
42
Peter
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