如何使用正则表达式词

Question

I was trying a simple regex code to match the following:

line = 'blah black blacksheep blah' 
if re.match(r'(\bblack\b)', line):
    print 'found it!

What am I doing wrong, I can't find "black" by itself?

Answer 1

From the docs :

re.match(pattern, string, flags=0)

If zero or more characters at the beginning of string match the regular expression pattern , return a corresponding MatchObject instance.

You probably want to use re.search or re.findall instead.

Answer 2

You should use re.search or re.findall here:

>>> strs = 'blah black blacksheep blah'
>>> re.search(r'\bblack\b', strs).group(0)
'black'

>>> re.findall(r'\bblack\b', strs)
['black']

Answer 3

You want re.search instead of re.match . From the docs :

7.2.5.3. search() vs. match()

Python offers two different primitive operations based on regular expressions: re.match() checks for a match only at the beginning of the string, while re.search() checks for a match anywhere in the string (this is what Perl does by default).

Answer 4

Use re.search() (returns None if no match on the whole string):

line = 'blah black blacksheep blah' 
if re.search(r'(\bblack\b)', line):
    print 'found it!