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Python - Regex Function

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• Python - Regex Function
  • Constructor
    • re.compile(pattern, flags=0)
  • Search
    • re.match(pattern, string, flags=0)
    • re.fullmatch(pattern, string, flags=0)
    • re.search(pattern, string, flags=0): Return 1st
  • Replace
    • re.sub(pattern, repl, string, count=0, flags=0)
    • re.subn(pattern, repl, string, count=0, flags=0)
  • Other
    • re.escape(pattern)
    • re.purge()
  • To List
    • re.findall(pattern, string, flags=0)
    • re.split(pattern, string, maxsplit=0, flags=0)
    • re.finditer(pattern, string, flags=0)

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Constructor

re.compile(pattern, flags=0)

• create a regular expression object used to match patterns in a string.

import re  # Importing re module
print("\n-------- re.compile(pattern, flags=0) --------\n")


# Defining regEx patterns
pattern = "amazing"
regex_object = re.compile(pattern)  # Createing a regEx object
text = "This tutorial is amazing!"   # String

# Searching for the pattern in the string
match_object = regex_object.search(text)
# Match Object: <re.Match object; span=(17, 24), match='amazing'>
print("Match Object:", match_object)

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Search

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

• mateches the pattern from the beginning of the string.

• Parameters

  • pattern: the regular expression to be matched
  • string: the string compared to the pattern at the start of the string.
  • flags: Bitwise OR (|) can be used to express multiple flags

• Return

  • Returns a match object if any match is found with information like start, end, span, etc.
  • Returns a None value in the case no match is found

import re  # Importing re module
print("\n-------- re.match(pattern, string, flags=0) --------\n")

print(re.match(r".?o", "dog"))  # <re.Match object; span=(0, 2), match='do'>
print(re.match("d", "dog"))     # <re.Match object; span=(0, 1), match='d'>
print(re.match("o", "dog"))     # None match='o'>

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

• matches the whole string with the pattern.

• Parameters

  • pattern: the regular expression to be matched.
  • string: The string to be searched for the pattern wherever within it.
  • flags: Bitwise OR (|) can be used to express multiple flags.

• Returns

  • a corresponding match object.
  • None if no match is found.

import re  # Importing re module
print("\n-------- re.fullmatch(pattern, string, flags=0) --------\n")

# Sample string
line = "Hello world"

# Using re.fullmatch()
print(re.fullmatch("Hello", line))      # None
print(re.fullmatch("Hello world", line))    # <re.Match object; span=(0, 11), match='Hello world'>

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re.search(pattern, string, flags=0): Return 1st

• look for the first occurrence of a regular expression sequence and deliver it.

• It will verify all rows of the supplied string, unlike Python’s re.match().

• Parameters

  • pattern: the regular expression to be matched.
  • string: The string to be searched for the pattern wherever within it.
  • flags: Bitwise OR (|) can be used to express multiple flags.
• Return:
  • If there is more than one match, only the first occurrence of the match will be returned.
  • If no matches are found, the value None is returned.

import re  # Importing re module
print("\n-------- re.search(pattern, string, flags=0) --------\n")

print(re.search(r".?o", "dog"))  # <re.Match object; span=(0, 2), match='do'>
print(re.search("d", "dog"))     # <re.Match object; span=(0, 1), match='d'>
print(re.search("o", "dog"))     # <re.Match object; span=(1, 2), match='o'>

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Replace

re.sub(pattern, repl, string, count=0, flags=0)

• substitutes the matching pattern with the new string

• Parameter:

  • Pattern: a regex pattern to be matched
  • repl: the “replacement” which replaces the pattern in string.
  • Count: control the number of substitutions

• Return:

  • the replaced string

import re  # Importing re module
print("\n-------- re.sub(pattern, repl, string, count=0, flags=0) --------\n")

print(re.sub("\s", "9", "The rain in Spain"))
# The9rain9in9Spain

print(re.sub("\s", "9", "The rain in Spain", 2))
# The9rain9in Spain

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re.subn(pattern, repl, string, count=0, flags=0)

• Working of subn if same as sub-function
• It returns a tuple

import re  # Importing re module
print("\n-------- re.subn(pattern, repl, string, count=0, flags=0) --------\n")

print(re.subn("\s", "9", "The rain in Spain"))
# ('The9rain9in9Spain', 3)

print(re.subn("\s", "9", "The rain in Spain", 2))
# ('The9rain9in Spain', 2)

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Other

re.escape(pattern)

• escapes the special character in the pattern.
• The esacpe function become more important when the string contains regular expression metacharacters in it.

import re  # Importing re module
print("\n-------- re.escape(pattern) --------\n")

print(re.escape('https://www.javatpoint.com/'))     # https://www\.javatpoint\.com/

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re.purge()

• clears the regular expression cache.

import re  # Importing re module
print("\n-------- re.purge() --------\n")

# Define some regular expressions
pattern1 = r'\d+'
pattern2 = r'[a-z]+'

# Use the regular expressions
# <re.Match object; span=(0, 3), match='123'>
print(re.search(pattern1, '123abc'))
# <re.Match object; span=(3, 6), match='abc'>
print(re.search(pattern2, '123abc'))

# Clear the regular expression cache
re.purge()

# Use the regular expressions again
# <re.Match object; span=(0, 3), match='456'>
print(re.search(pattern1, '456def'))
# <re.Match object; span=(3, 6), match='def'>
print(re.search(pattern2, '456def'))

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To List

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

• Return all non-overlapping matches of pattern in string, as a list of strings or tuples.

print(re.findall(r'',"which foot or hand fell fastest"))
# ['', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '']
print(re.findall(r'o',"which foot or hand fell fastest"))
# ['o', 'o', 'o']

print(re.findall(r'\bf[a-z]*', 'which foot or hand fell fastest'))
# ['foot', 'fell', 'fastest']

print(re.findall(r'(\w+)=(\d+)', 'set width=20 and height=10'))
# [('width', '20'), ('height', '10')]

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re.split(pattern, string, maxsplit=0, flags=0)

• splits the pattern by the occurrences of patterns.
• If maxsplit is zero, then the maximum number of splits occurs.
• If maxsplit is one, then it splits the string by the first occurrence of the pattern and returns the remaining string as a final result.

import re  # Importing re module
print("\n-------- re.split(pattern, string, maxsplit=0, flags=0) --------\n")

print(re.split("\s", "The rain in Spain"))
# ['The', 'rain', 'in', 'Spain']

print(re.split("\s", "The rain in Spain", maxsplit=1))
# ['The', 'rain in Spain']

print(re.split("\s", "The rain in Spain", maxsplit=2))
# ['The', 'rain', 'in Spain']

print(re.split("\s", "The rain in Spain", maxsplit=3))
# ['The', 'rain', 'in', 'Spain']

print(re.split("\s", "The rain in Spain", maxsplit=4))
# ['The', 'rain', 'in', 'Spain']

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

• Returns an iterator that yields all non-overlapping matches of pattern in a string.

• String is scanned from left to right.

• Parameters

  • pattern: the regular expression to be matched.
  • string: The string to be searched for the pattern wherever within it.
  • flags: Bitwise OR (|) can be used to express multiple flags.
• Returns
  • a corresponding match object.
  • None if no match is found.

import re  # Importing re module
print("\n-------- re.finditer(pattern, string, flags=0) --------\n")

# Using re.finditer()
iter_ = re.finditer(r'[aeiou]', "Hello world. I am Here!")

# Iterating the itre_
for i in iter_:
    print(i)

# <re.Match object; span=(1, 2), match='e'>
# <re.Match object; span=(4, 5), match='o'>
# <re.Match object; span=(7, 8), match='o'>
# <re.Match object; span=(15, 16), match='a'>
# <re.Match object; span=(19, 20), match='e'>
# <re.Match object; span=(21, 22), match='e'>

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