Python正则表达式不匹配

Question

This is one of those things where I'm sure I'm missing something simple, but... In the sample program below, I'm trying to use Python's RE library to parse the string "line" to get the floating-point number just before the percent sign, ie "90.31". But the code always prints "no match".

I've tried a couple other regular expressions as well, all with the same result. What am I missing?

#!/usr/bin/python
import re
line = '    0 repaired, 90.31% done'
pct_re = re.compile(' (\d+\.\d+)% done$')
#pct_re = re.compile(', (.+)% done$')
#pct_re = re.compile(' (\d+.*)% done$')
match = pct_re.match(line)
if match: print 'got match, pct=' + match.group(1)
else: print 'no match'

Answer 1

match only matches from the beginning of the string. Your code works fine if you do pct_re.search(line) instead.

Answer 2

You should use re.findall instead:

>>> line = '    0 repaired, 90.31% done'
>>> 
>>> pattern = re.compile("\d+[.]\d+(?=%)")
>>> re.findall(pattern, line)
['90.31']

re.match will match at the start of the string. So you would need to build the regex for complete string.

Answer 3

try this if you really want to use match:

re.match(r'.*(\d+\.\d+)% done$', line)

r'...' is a "raw" string ignoring some escape sequences, which is a good practice to use with regexp in python. – kratenko (see comment below)