Newbie: is a variable defined?

[Lemniscate]

Oh, the reason I like dir() better than locals is that locals() is a
dictionary and I didn't see the need in accessing all the values (its
slightly more efficient, on huge lists of local items, that have
large/long values, on slow computers, etc.l alternatively, you could
query locals().keys() or use something like
locals().has_key(Your_Variable) ).  I just wanted to give you some
options.  Good luck.

Chris


Nicodemus <nicodemus at globalite.com.br> wrote in message news:<mailman.1040413473.24131.python-list at python.org>...
> Christopher Swingley wrote:
> 
> >Greetings,
> >
> >
> >Longer version: What I'm trying to do is parse a file that may or may 
> >not contain an email address.  If it does, I use regular expressions to 
> >extract the username portion of the email address and place this in a 
> >variable named 'efrom'.  Later, I want to search a SQL database, and if 
> >'efrom' has been defined it will perform one SELECT and if it's not 
> >it'll do something else.
> >
> >I could set up a seperate flag 'efrom_defined = 0', update it when efrom 
> >gets a value, and then test this flag.  Or I could use a 'try: except 
> >NameError:' block.  Or I could do 'efrom = ""' at the beginning of the 
> >program and then test 'if len(efrom):'
> >
> >How would you do this?
> >
> 
> Hail!
> 
> You can do what you want by checking if the variable has an entry in the 
> locals dir:
> 
>  >>> 'efrom' in locals()
>  0
>  >>> efrom = 10
>  >>> 'efrom' in locals()
> 1
> 
> But I would recommend against that.
> 
> The standard way is to initialize all the variables with None, and then 
> check later if they were
> initialized with something else.
> 
>  >>> efrom = None
>  >>> efrom = 'xx at xx.com'
>  # later...
>  >>> if efrom is not None:
> ...    # use 'efrom' variable here
> 
> 
> 
> Farewell,
> Nicodemus.