str = ‘an example word:cat!!‘ match = re.search(r‘word:\w\w\w‘, str) # If-statement after search() tests if it succeeded if match: print ‘found‘, match.group() ## ‘found word:cat‘ else: print ‘did not find‘
## The code match = re.search(pat, str) stores the search result in a variable named "match". Then the if-statement tests the match -- if true the search succeeded and match.group() is the
matching text (e.g. ‘word:cat‘).
## The ‘r‘ at the start of the pattern string designates a python "raw" string which passes through backslashes without change which is very handy for regular expressions (Java needs this feature badly!). I recommend that
you always write pattern strings with the ‘r‘ just as a habit.
基本的模式/Basic Patterns:
a, X, 9, < ##-- ordinary characters just match themselves exactly. The meta-characters which do not match themselves because they have special meanings are: . ^ $ * + ? { [ ] \ | ( ) (details below)
. (a period) ##-- matches any single character except newline ‘\n‘
\w ##-- (lowercase w) matches a "word" character: a letter or digit or underbar [a-zA-Z0-9_]. Note that although "word" is the mnemonic for this, it only matches a single word char, not a whole word. \W (upper case W) matches
any non-word character.
\b ##-- boundary between word and non-word
\s ##-- (lowercase s) matches a single whitespace character -- space, newline, return, tab, form [ \n\r\t\f]. \S (upper case S) matches any non-whitespace character.
\t, \n, \r ##-- tab, newline, return
\d ##-- decimal digit [0-9] (some older regex utilities do not support but \d, but they all support \w and \s)
^ = start, $ = end ##-- match the start or end of the string
\ ##-- inhibit the "specialness" of a character. So, for example, use \. to match a period or \\ to match a slash. If you are unsure if a character has special meaning, such as ‘@‘, you can put a slash in front of it, \@,
to make sure it is treated just as a character.
基本规则：
1） search的过程是从一个字符串的头到尾进行的，但发现第一个匹配项时停止
2）如果 match = re.search(pat,str) 成功了，match的值为非None值，并且 match.group()中存放着匹配项
## Search for pattern ‘iii‘ in string ‘piiig‘. ## All of the pattern must match, but it may appear anywhere. ## On success, match.group() is matched text. match = re.search(r‘iii‘, ‘piiig‘) => found, match.group() == "iii" match = re.search(r‘igs‘, ‘piiig‘) => not found, match == None ## . = any char but \n match = re.search(r‘..g‘, ‘piiig‘) => found, match.group() == "iig" ## \d = digit char, \w = word char match = re.search(r‘\d\d\d‘, ‘p123g‘) => found, match.group() == "123" match = re.search(r‘\w\w\w‘, ‘@@abcd!!‘) => found, match.group() == "abc"
## i+ = one or more i‘s, as many as possible. match = re.search(r‘pi+‘, ‘piiig‘) => found, match.group() == "piii" ## Finds the first/leftmost solution, and within it drives the + ## as far as possible (aka ‘leftmost and largest‘). ## In this example, note that it does not get to the second set of i‘s. match = re.search(r‘i+‘, ‘piigiiii‘) => found, match.group() == "ii" ## \s* = zero or more whitespace chars ## Here look for 3 digits, possibly separated by whitespace. match = re.search(r‘\d\s*\d\s*\d‘, ‘xx1 2 3xx‘) => found, match.group() == "1 2 3" match = re.search(r‘\d\s*\d\s*\d‘, ‘xx12 3xx‘) => found, match.group() == "12 3" match = re.search(r‘\d\s*\d\s*\d‘, ‘xx123xx‘) => found, match.group() == "123" ## ^ = matches the start of string, so this fails: match = re.search(r‘^b\w+‘, ‘foobar‘) => not found, match == None ## but without the ^ it succeeds: match = re.search(r‘b\w+‘, ‘foobar‘) => found, match.group() == "bar"
str = ‘purple alice-b@google.com monkey dishwasher‘ match = re.search(r‘\w+@\w+‘, str) if match: print match.group() ## ‘b@google‘
## Square brackets can be used to indicate a set of chars, so [abc] matches ‘a‘ or ‘b‘ or ‘c‘. The codes \w, \s etc. work inside square brackets too with the one exception that dot (.) just means a literal dot. For the emails problem, the square brackets are an easy way to add ‘.‘ and ‘-‘ to the set of chars which can appear around the @ with the pattern r‘[\w.-]+@[\w.-]+‘ to get the whole email address:
match = re.search(r‘[\w.-]+@[\w.-]+‘, str) if match: print match.group() ## ‘alice-b@google.com‘
str = ‘purple alice-b@google.com monkey dishwasher‘ match = re.search(‘([\w.-]+)@([\w.-]+)‘, str) if match: print match.group() ## ‘alice-b@google.com‘ (the whole match) print match.group(1) ## ‘alice-b‘ (the username, group 1) print match.group(2) ## ‘google.com‘ (the host, group 2) ##Tips: A common workflow with regular expressions is that you write a pattern for the thing you are looking for, adding parenthesis groups to extract the parts you want.
## Suppose we have a text with many email addresses str = ‘purple alice@google.com, blah monkey bob@abc.com blah dishwasher‘ ## Here re.findall() returns a list of all the found email strings emails = re.findall(r‘[\w\.-]+@[\w\.-]+‘, str) ## [‘alice@google.com‘, ‘bob@abc.com‘] for email in emails: # do something with each found email string print email
# Open file f = open(‘test.txt‘, ‘r‘) # Feed the file text into findall(); it returns a list of all the found strings strings = re.findall(r‘some pattern‘, f.read())
str = ‘purple alice@google.com, blah monkey bob@abc.com blah dishwasher‘ tuples = re.findall(r‘([\w\.-]+)@([\w\.-]+)‘, str) print tuples ## [(‘alice‘, ‘google.com‘), (‘bob‘, ‘abc.com‘)] for tuple in tuples: print tuple[0] ## username print tuple[1] ## host
str = ‘purple alice@google.com, blah monkey bob@abc.com blah dishwasher‘ ## re.sub(pat, replacement, str) -- returns new string with all replacements, ## \1 is group(1), \2 group(2) in the replacement print re.sub(r‘([\w\.-]+)@([\w\.-]+)‘, r‘\1@yo-yo-dyne.com‘, str) ## purple alice@yo-yo-dyne.com, blah monkey bob@yo-yo-dyne.com blah dishwasher
原文：http://blog.csdn.net/tao_sun/article/details/18794057