8.12.3 Other Search Functions; Accessing Matches

Function search—Finding the First Match Anywhere in a String

• search looks in a string for the first occurrence of a substring that matches a regular expression and returns a match object (of type SRE_Match) that contains the matching substring
• Match object’s group method returns that substring

import re

result = re.search('Python', 'Python is fun')

result.group() if result else 'not found'

• search returns None if the string does not contain the pattern

result2 = re.search('fun!', 'Python is fun')

result2.group() if result2 else 'not found'

• Can search for a match only at the beginning of a string with function match

Ignoring Case with the Optional flags Keyword Argument

• Many re module functions receive an optional flags keyword argument
• Changes how regular expressions are matched

result3 = re.search('Sam', 'SAM WHITE', flags=re.IGNORECASE)

result3.group() if result3 else 'not found'

Metacharacters That Restrict Matches to the Beginning or End of a String

• ^ metacharacter at the beginning of a regular expression (and not inside square brackets) is an anchor
• Indicaties that the expression matches only the beginning of a string

result = re.search('^Python', 'Python is fun')

result.group() if result else 'not found'

result = re.search('^fun', 'Python is fun')

result.group() if result else 'not found'

• $ metacharacter at the end of a regular expression is an anchor indicating that the expression matches only the end of a string

result = re.search('Python$', 'Python is fun')

result.group() if result else 'not found'

result = re.search('fun$', 'Python is fun')

result.group() if result else 'not found'

Function findall and finditer—Finding All Matches in a String

• findall finds every matching substring in a string
• Returns a list of the matching substrings

contact = 'Wally White, Home: 555-555-1234, Work: 555-555-4321'

re.findall(r'\d{3}-\d{3}-\d{4}', contact)

• finditer works like findall, but returns a lazy iterable of match objects

for phone in re.finditer(r'\d{3}-\d{3}-\d{4}', contact):
    print(phone.group())

Capturing Substrings in a Match

• Use parentheses metacharacters—( and )—to capture substrings in a match

text = 'Charlie Cyan, e-mail: demo1@deitel.com'

pattern = r'([A-Z][a-z]+ [A-Z][a-z]+), e-mail: (\w+@\w+\.\w{3})'

result = re.search(pattern, text)

• The regular expression specifies two substrings to capture, each denoted by the metacharacters ( and )
• ( and ) do not affect whether the pattern is found in the string text
• match function returns a match object only if the entire pattern is found in the string text
• match object’s groups method returns a tuple of the captured substrings

result.groups()

• match object’s group method returns the entire match as a single string

result.group()

• Access each captured substring by passing an integer to the group method

result.group(1)

result.group(2) 

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