Lesson 24:

RegEx groups and the Pipe Character

Regex can also be used in other ways, such as partial matching.



In [4]:

    
import re

phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')
phoneNumRegex.search('My number is 415-555-4242') # returns a match object
mo = phoneNumRegex.search('My number is 415-555-4242') # store match object
mo.group() # print matched strings in match object









    Out[4]:





'415-555-4242'

To get different sections of a string, we can use groups via parenthesis:



In [12]:

    
phoneNumRegex = re.compile(r'(\d\d\d)-(\d\d\d-\d\d\d\d)') # The first () is group 1, the second () is group 2
phoneNumRegex.search('My number is 415-555-4242') # returns a match object with subgroups
mo = phoneNumRegex.search('My number is 415-555-4242') # store match object with subgroups
print('The area code is ' + mo.group(1)) # print out the subgroup matching the parameter
print('The rest of it is ' + mo.group(2)) # print out the other subgroup









    



The area code is 415
The rest of it is 555-4242

If parenthesis are actually part of the pattern, they need to be escaped:



In [18]:

    
phoneNumRegex = re.compile(r'\(\d\d\d\)-\d\d\d-\d\d\d\d')

mo = phoneNumRegex.search('My number is 415-555-4242') # returns no match
print(mo)
mo =phoneNumRegex.search('My number is (415)-555-4242') # returns a match object
mo.group()









    



None






    Out[18]:





'(415)-555-4242'

The '|' RegEx Operater

The pipe character, |, matches one of several patterns in a group.



In [27]:

    
batRegex = re.compile(r'Bat(man|mobile|copter|cat)') # The pipe character seperates the suffixes, and allows any match.

mo = batRegex.search('Batmobile lost a wheel.')
print(mo.group()) # Print matching string

print(mo.group(1)) # Pass variable 1 into the group function to find which suffix group actually matched

#mo2 = batRegex.search('Batmotorcycle lost a wheel.')
#mo.group() # will return error because no match









    



Batmobile
mobile

Recap

Groups are created in regex strings with parentheses ().
The first set of parenthesis is group 1, the second is 2, and so on.
Calling .group() or .group(0) returns the full matching string, .group(1) returns the actual matching group.
Use \( and \) to escape parenthesis in a regex string, otherwise they will be treated as groups.
The | pipe character can match any one of many possible groups.