[Tutor] all elements equal in tuple or list

[Bob Gailer]

At 07:24 PM 11/18/2004, Jacob S. wrote:
>My name's not Kent, but...
>
> >def test(vals):
> >     if vals:
> >         i = iter(vals)
> >         first = i.next()
> >         for item in i:
> >             if first != item:
> >                 return False
> >     return True
>
>The if vals: is an interesting idea... If no comparison operators are
>entered after a variable, the interpreter automatically checks to see if the
>variable returns true. So if vals returns true, then the code block beneath
>it is executed.

To be more explicit (quoting from the manual) "when expressions are used by 
control flow statements, the following values are interpreted as false: 
None, numeric zero of all types, empty sequences (strings, tuples and 
lists), and empty mappings (dictionaries). All other values are interpreted 
as true."

Whatever follows - if - is taken as an expression, evaluated, then 
interpreted as stated above.

The reason for doing this is: if vals is an empty sequence, iter(vals) will 
raise the StopIteration exception.

>Otherwise, the function returns True.
>All that does is check to see that vals is not an empty list. (Therefore
>returning False)
>
>Empty tuples,lists,dictionaries,strings,etc. return False ex. (),[],{},""
>If they have anything in them, they return True ex.
>(''),["hello"],{"Jacob",3},"A"
>
>Nonzero integers,floats,complex numbers,Long integers, etc. return True
>All others  return True
>
>
>
>
>
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Bob Gailer
bgailer at alum.rpi.edu
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