Check if a string is hexadecimal

Question

I know the easiest way is using a regular expression, but I wonder if there are other ways to do this check.

Why do I need this? I am writing a Python script that re

Answer 1

Most of the solutions proposed above do not take into account that any decimal integer may be also decoded as hex because decimal digits set is a subset of hex digits set. So Python will happily take 123 and assume it's 0123 hex:

>>> int('123',16)
291

This may sound obvious but in most cases you'll be looking for something that was actually hex-encoded, e.g. a hash and not anything that can be hex-decoded. So probably a more robust solution should also check for an even length of the hex string:

In [1]: def is_hex(s):
   ...:     try:
   ...:         int(s, 16)
   ...:     except ValueError:
   ...:         return False
   ...:     return len(s) % 2 == 0
   ...: 

In [2]: is_hex('123')
Out[2]: False

In [3]: is_hex('f123')
Out[3]: True