How to detect list versus string

Peter Otten __peter__ at web.de
Fri Jun 11 19:15:20 CEST 2004


Jonathon McKitrick wrote:

> 
> This sounds simpler that it is, hopefully  ;-)
> 
> I have a method that builds a dynamic combo box.  Before I do that, I set
> a class variable to the new list of items.
> 
> def make_new_cat_box(self, cats):
      if isinstance(cats, basestring):
          cats = [cats]
>     self.cat_list = cats
> 
> Sounds simple.  But sometimes, my combo box will only have one choice
> available.  When I call this method with a list of one string, the string
> is split up, and my combo box now has a separate item for each letter in
> the
> string.  What I obviously want to do is detect when the object coming in
> is
> a list or a string.  type() isn't as useful as I had hoped, and len() will

>>> value = "123"
>>> if type(value) == type(""):
...     print "It's a string"
...
It's a string
>>>

> give me the length of the string, so I cannot tell if it is a string or a
> list of more that one item.
> 
> There has to be a simple solution.


I'd prefer isinstance() over type(cats) == type(""). If you are sure there
won't be any unicode strings you can use isinstance(cats, str) instead of
the basestring variant shown above.

Peter



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