srtring to int question

[Alex Martelli]

"Jim Richardson" <warlock at eskimo.com> wrote in message
news:slrn8pbuah.1t3.warlock at gargoyle.myth...
    [snip]
>  OK, the question, I use raw_input to poll for the julian day, and
> then convert to int via int, but how do I check that the value from
raw_input
> is "intable"? that is, it works fine if I pass a number, but if I type in
> non-numerical characters, [a-zA-Z!@# etc] then the code errors on the
> int() function. Any pointers? thanks

You can use several approaches.  Most idiomatic is perhaps:

    try:
        result=int(astring)
    except ValueError:
        result=0

or similar.  I.e., the "it's easier to ask forgiveness than
permission" idiom (from Grace Murray Hopper's best-known
quote): try the operation, catch the exception if it fails;
it's easier than checking beforehand if the operation's
pre-requisites are in fact entirely satisfied.

In this specific case, the pre-reqs are simple enough that
you may choose to check them; as you're not interested in
negative numbers, you may want to accept just a string of
digits, easily checked with re.  But I think try/except is
a better general idiom for such needs in Python.


Alex