Python regular expression
A regular articulation is an extraordinary succession of characters that encourages you effectively check if a string matches an example.
Python has included the re module since form 1.5, which gives a Perl-style regular articulation design.
The
re module gives the Python language loaded with standard articulation usefulness.
The
compile work produces a regular articulation object dependent on an example string and discretionary banner parameters. This article has a lot of techniques for customary articulation coordinating and substitution.
The
re module additionally furnishes capacities that are completely useful with these strategies, utilizing an example string as their first contention.
This part centers around regular articulation preparing capacities usually utilized in Python.
re.match function
re.match attempts to match a pattern from the beginning of the string. If the start position is not matched successfully, match() returns none.
Function syntax:
re.match(pattern, < /span>string, flags =0)
Function parameter description:
| Parameters | Description |
| pattern | matching customary expressions |
| string | The string to coordinate. |
The | flags | banner is utilized to control how standard articulations are coordinated, for example, regardless of whether to recognize capitalized and lowercase, multi-line coordinating, etc. See: Regular Expression Modifiers - Optional Flags |
The coordinating achievement re.match strategy restores a coordinating article, else it returns None.
We can utilize the group(num) or gatherings() coordinating article capacities to get the coordinating articulation.
| Matching object methods | Description |
| group(num=0) | matches the string of the whole articulation, gathering() can enter different gathering numbers at once, in which case it will return one containing those The tuple of the esteem relating to the gathering. |
| groups() | Returns a tuple containing all the gathering strings, from 1 to the included group number. |
Instance
import re
print(re.match('www', 'www.welookups.com').span())
print(re.match('com', 'www.welookups.com'))
The above example runs the output as:
(0, 3)
None
Instance
import re
line = "Cats are smarter than dogs"
matchObj = re.match( r'(.*) are (.*?) .*', line, re.M|re.I)
if matchObj:
print "matchObj.group() : ", matchObj.group()
print "matchObj.group(1) : ", matchObj.group(1)
print "matchObj.group(2) : ", matchObj.group(2)
else:
print "No match!!"
The above example execution results are as follows：
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats
matchObj.group(2) : smarter
re.search method
re.search scans the entire string and returns the first successful match.
Function syntax:
re.search(pattern, < /span>string, flags =0)
Function parameter description:
| Parameters | Description |
| pattern | matching regular expressions |
| string | The string to coordinate. |
The | flags | banner is utilized to control how ordinary articulations are coordinated, for example, regardless of whether to recognize capitalized and lowercase, multi-line coordinating, etc. |
Successful match The re.search strategy restores a coordinating item, else it returns None.
We can utilize the group(num) or gatherings() coordinating item capacities to get the coordinating articulation.
| Matching object methods | Description |
| group(num=0) | matches the string of the whole articulation, gathering() can enter different gathering numbers at once, in which case it will return one containing those The tuple of the esteem relating to the gathering. |
| groups() | Returns a tuple containing all the gathering strings, from 1 to the included group number. |
Instance
import re
print(re.search('www', 'www.welookups.com').span())
print(re.search('com', 'www.welookups.com').span())
The above precedent runs the yield as:
(0, 3)
(11, 14)
instance
import re
line = "Cats are smarter than dogs";
searchObj = re.search( r'(.*) are (.*?) .*', line, re.M|re.I)
if searchObj:
print "searchObj.group() : ", searchObj.group()
print "searchObj.group(1) : ", searchObj.group(1)
print "searchObj.group(2) : ", searchObj.group(2)
else:
print "Nothing found!!"
The above example execution results are as follows:
searchObj.group() : Cats are smarter than dogs
searchObj.group(1) : Cats
searchObj.group(2) : smarter
The difference between re.match and re.search
re.match only matches the beginning of the string. If the string does not match the regular expression, the match fails, the function returns None; and re.search matches the entire string until a match is found.
Instance
import re
line = "Cats are smarter than dogs";
matchObj = re.match( r'dogs', line, re.M|re.I)
if matchObj:
print "match --> matchObj.group() : ", matchObj.group()
else:
print "No match!!"
matchObj = re.search( r'dogs', line, re.M|re.I)
if matchObj:
print "search --> matchObj.group() : ", matchObj.group()
else:
print "No match!!"
The above model keeps running as pursues:
No match!!
look - - > matchObj.group() : dogs
Search and Replace
Python's re module gives re.sub to supplanting matches in strings.
Syntax:
re.sub(pattern, repl, string, count=0, flags=0)
Parameters:
- pattern : The example string in the standard.
-
Repl : The supplanted string, which can likewise be a capacity.
-
String : The first string to be supplanted by the query.
-
Tally : The most extreme number of substitutions after example coordinating. The default 0 intends to supplant all matches.
Instance
import re
phone = "2004-959-559 # This is a foreign phone number"
num = re.sub(r'#.*$', "", phone)
print "phone number is: ", num
num = re.sub(r'\D', "", phone)
print "phone number is : ", num
The above example execution results are as follows:
phone number is: 2004-959-559
phone number is : 2004959559
repl The argument is a function
Multiply the number in the string by 2 in the following example:
Instance
import re
def double(matched):
value = int(matched.group('value'))
return str(value * 2)
s = 'A23G4HFD567'
print(re.sub('(?P<value>\d+)', double, s))
Execution output is:
A46G8HFD1134
re.compile function
The
compile function is used to compile a regular expression and generate a regular expression (pattern ) object for use by the match() and search() functions.
The syntax is:
Parameters:
-
pattern : A regular expression in the form of a string
-
flags : Optional, indicating matching mode, such as ignoring case, multi-line mode, etc. The specific parameters are:
-
re.I ignore case
-
re.L indicates that the special character set \w, \W, \b, \B, \s, \S depends on the current environment
-
re.M multi-line mode
-
re.S is . and includes any characters including line breaks (. not included Line breaks)
-
re.U indicates that the special character set \w, \W, \b, \B, \d, \D, \s, \S depends on the Unicode character property database
-
re.X For readability, ignore spaces and comments after #
>
Instance
Instance
>>>import re
>>> pattern = re.compile(r'\d+')
>>> m = pattern.match('one12twothree34four')
>>> print m
None
>>> m = pattern.match('one12twothree34four', 2, 10)
>>> print m
None
>>> m = pattern.match('one12twothree34four', 3, 10)
>>> print m
lt;_sre.SRE_Match object at 0x10a42aac0>
>>> m.group(0)
'12'
>>> m.start(0)
3
>>> m.end(0)
5
>>> m.span(0)
(3, 5)
In the above, a Match object is returned when the match is successful, where:
group([group1, ...]) method is used to get one or more group matching strings. When you want to get the entire matching substring, you can use group directly. ) or group(0);start([group]) method is used to get the starting position of the substring of the group matching in the entire string (the index of the first character of the substring). The default value of the parameter is 0. ;end([group]) method is used to get the end position of the substring of the packet matching in the entire string (index +1 of the last character of the substring). The default value of the parameter is 0. ;span([group]) method returns (start(group), end(group)).
Look at an example:
Instance
>>>import re
>>> pattern = re.compile(r'([a-z]+) ([a-z]+)', re.I)
>>> m = pattern.match('Hello World Wide Web')
>>> print m
<_sre.SRE_Match object at 0x10bea83e8>
>>> m.group(0)
'Hello World'
>>> m.span(0)
(0, 11)
>>> m.group(1)
'Hello'
>>> m.span(1)
(0, 5)
>>> m.group(2)
'World'
>>> m.span(2)
(6, 11)
>>> m.groups()
('Hello', 'World')
>>> m.group(3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: no such group
findall
Find all substrings matched by the regular expression in the string and return a list, or an empty list if no match is found.
Note: match and search are matched once and findall matches all.
The syntax is:
findall(string[, pos[, endpos]])
Parameters:
- string : The string to be matched.
- pos : An optional parameter that specifies the starting position of the string. The default is 0.
-
endpos : An optional parameter that specifies the end of the string. The default is the length of the string.
Find all the numbers in the string:
Instance
import re
pattern = re.compile(r'\d+')
result1 = pattern.findall('welookups 123 google 456')
result2 = pattern.findall('we88lookups123google456', 0, 10)
print(result1)
print(result2)
Output results:
['123', '456']
['88', '12']
re.finditer
Similar to findall, find all substrings that the regular expression matches in the string and return them as an iterator.
re.finditer(pattern, string, flags=0)