Regex for fixed width field

Question

I need to match a fixed width field on a file layout with a regular expression. The field is numeric/integer, always have four characters and is included in the range of 0..

Answer 1

This seems too easy, am I understanding the problem correctly?

\[01][0-9]{3}\

I don't know what .. means, integer in range? That must be a perlism or something.

This seems to work the way you want to me:

In [3]: r = re.compile(r'[01][0-9]{3}')

In [4]: r.match('0001')
Out[4]: <_sre.SRE_Match object at 0x2fa2d30>

In [5]: r.match('1001')
Out[5]: <_sre.SRE_Match object at 0x2fa2cc8>

In [6]: r.match('2001')

In [7]: r.match('001')

In [8]: