How to check if a string "is" an int?

[Paul Rubin]

"Fredrik Lundh" <fredrik at pythonware.com> writes:
> no, but all characters in the string belongs to the "digit" character
> class, which is what the "is" predicates look for.

That description is not quite right.  All characters in the empty
string belong to the "digit" character class, but isdigit returns
false (which it probably should).

    Python 2.3.4 (#1, Feb  2 2005, 12:11:53)
    [GCC 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> ''.isdigit()
    False