Home Original page

does a variable exist

Darrell news at dorb.com
Fri Jan 7 21:46:39 EST 2000 
"Wm. King" <wjk at wjk.mv.com> wrote in message
news:38767A50.CFDEC3C2 at wjk.mv.com...
> Could you do something like:
>
> try:
>     print x
> except NameError:
>    print "No global or local x"
>
> Just wondering?
>

Yulp.
You see that a lot for imports also.
try:
    from _socket import *
except ImportError:
    from socket import *

Throwing exceptions takes time. Not a problem for imports but might be a
problem when accessing variables.

Here's another way to say the same thing.
>>> myVar=1
>>> import sys
>>> globals().get('myVar',None)
1
>>> globals().get('xxxx',None)
>>>
>>> class VarError:
...     def __init__(self, msg):
...             self._msg=msg
...     def __str__(self):
...             return self._msg
...
>>>
>>> print globals().get('xxxx',VarError("No global or local xxxx"))
No global or local xxxx
>>>

--
--Darrell
More information about the Python-list mailing list