Question

Python loves raising exceptions, which is usually great. But I’m facing some strings I desperately want to convert to integers using C’s atoi / atof semantics – e.g. atoi of “3 of 12”, “3/12”, “3 / 12”, should all become 3; atof(“3.14 seconds”) should become 3.14; atoi(” -99 score”) should become -99. Python of course has atoi and atof functions, which behave nothing like atoi and atof and exactly like Python’s own int and float constructors.

The best I have so far, which is really ugly and hard to extend to the various float formats available:

value = 1
s = str(s).strip()
if s.startswith("-"):
    value = -1
    s = s[1:]
elif s.startswith("+"):
    s = s[1:]
try:
    mul = int("".join(itertools.takewhile(str.isdigit, s)))
except (TypeError, ValueError, AttributeError):
    mul = 0
return mul * value

Answer 1

It’s pretty straightforward to do this with regular expressions:

>>> import re
>>> p = re.compile(r'[^\d-]*(-?[\d]+(\.[\d]*)?([eE][+-]?[\d]+)?)')
>>> def test(seq):
        for s in seq:
            m = p.match(s)
            if m:
                result = m.groups()[0]
                if "." in result or "e" in result or "E" in result:
                    print "{0} -> {1}".format(s, float(result))
                else:
                    print '"{0}" -> {1}'.format(s, int(result))
            else:
                print s, "no match"

>>> test(s)
"1 0" -> 1
"3 of 12" -> 3
"3 1/2" -> 3
"3/12" -> 3
3.15 seconds -> 3.15
3.0E+102 -> 3e+102
"what about 2?" -> 2
"what about -2?" -> -2
2.10a -> 2.1