what is wrong with this line? while (line = workfile.readline()) != "":

[erudite]

Thank you all for your responses. Question though. Is there some sort of
advantage to not allowing statements where a expressions is expected?

"D-Man" <dsh8290 at rit.edu> wrote in message
news:mailman.990546832.2115.python-list at python.org...
> On Tue, May 22, 2001 at 09:14:41AM -0600, erudite wrote:
> | Hey,
> |     I'm coming from the Java world to the python world which is probably
why
> | I'm a little confused as to why this statement doesn't work:
>
> Yep.
>
> | while (line = workfile.readline()) != "":
> |
> | when I try to run it I get a :
> |
> |   File "srns.py", line 38
> |     while (line = workfile.readline()) != "":
> |                 ^
> | SyntaxError: invalid syntax
>
> The difference :
>     In Java (and C and C++) assignment is an _expression_, and as such
>     it can occur anywhere an expression can occur (such as the
>     condition of a while loop).
>
>     In Python assignment is a _statement_ and can only occur where
>     statements can occur, not where an expression is expected.
>
>
> The proper way to write that loop is:
>
> while 1 :
>     line = workfile.readline()
>
>     if line == "" : break
>
>     <rest of loop here>
>
>
> This organization of the loop allows the advancement (reading a line)
> to exist only once.  If you note carefully there is only 1 entrance
> and only 1 exit point of the loop.
>
> An alternative way to write the loop:
>
> line = workfile.readline()
> while line != "" :
>     <rest of loop here>
>     line = workfile.readline()
>
> IMO this is a poorer way of organizing the loop due to the redunancy
> of the line containing the call to 'readline'.
>
>
> HTH,
> -D
>
>