Python Library Reference
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4.2.6 Examples

Python does not currently have an equivalent to scanf().  Regular expressions are generally more powerful, though also more verbose, than scanf() format strings. The table below offers some more-or-less equivalent mappings between scanf() format tokens and regular expressions.

scanf() Token	Regular Expression
%c	.
%5c	.{5}
%d	[-+]\d+
%e, %E, %f, %g	[-+](\d+(\.\d*)?|\d*\.\d+)([eE]\d+)?
%i	[-+](0[xX][\dA-Fa-f]+|0[0-7]*|\d+)
%o	0[0-7]*
%s	\S+
%u	\d+
%x, %X	0[xX][\dA-Fa-f]

To extract the filename and numbers from a string like

    /usr/sbin/sendmail - 0 errors, 4 warnings

you would use a scanf() format like

    %s - %d errors, %d warnings

The equivalent regular expression would be

    (\S+) - (\d+) errors, (\d+) warnings

If you create regular expressions that require the engine to perform a lot of backtracking, you may encounter a RuntimeError exception with the message maximum recursion limit exceeded. For example,

>>> s = "<" + "that's a very big string!"*1000 + ">"
>>> re.match('<.*?>', s)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/local/lib/python2.3/sre.py", line 132, in match
    return _compile(pattern, flags).match(string)
RuntimeError: maximum recursion limit exceeded

You can often restructure your regular expression to avoid backtracking. The above regular expression can be recast as <[^>]*>. As a further benefit, such regular expressions will run faster than their backtracking equivalents.