Return value of an assignment statement?

[Jeff Schwab]

Jeff Schwab wrote:
> mrstephengross wrote:
>> Hi all. In C, an assignment statement returns the value assigned. For
>> instance:
>>
>>   int x
>>   int y = (x = 3)
>>
>> In the above example, (x=3) returns 3, which is assigned to y.
>>
>> In python, as far as I can tell, assignment statements don't return
>> anything:
>>
>>   y = (x = 3)
>>
>> The above example generates a SyntaxError.
>>
>> Is this correct? I just want to make sure I've understood the
>> semantics.
> 
> Yes, but there is valid syntax for the common case you mentioned:
> 
>     y = x = 3
> 
> What you can't do (that I really miss) is have a tree of assign-and-test 
> expressions:
> 
>     import re
>     pat = re.compile('some pattern')
> 
>     if m = pat.match(some_string):
>         do_something(m)
>     else if m = pat.match(other_string):
>         do_other_thing(m)
>     else:
>         do_default_thing()


This is apparently section 1.9 of the Python Cookbook:

http://www.oreilly.com/catalog/pythoncook2/toc.html

Martelli suggests something similar to the "thigamabob" technique I use 
(he calls it DataHolder).  It's really more like the "xmatch" posted by 
Paul Rubin.

Martelli also says, though, that if you need this, you're not thinking 
Pythonically.  I don't know what the Pythonic alternative is.  The 
iterating-over-pairs approach suggested by Bruno is the only alternative 
I've seen.