re.sub() - Python RegEx Last Updated : 10 Dec, 2024 Comments Improve Suggest changes Like Article Like Report re.sub() method in Python parts of a string that match a given regular expression pattern with a new substring. This method provides a powerful way to modify strings by replacing specific patterns, which is useful in many real-life tasks like text processing or data cleaning. Python import re a = "apple orange apple banana" pattern = "apple" repl = "grape" # Replace all occurrences of "apple" with "grape" result = re.sub(pattern, repl, a) print(result) Outputgrape orange grape banana Table of ContentSyntax of re.sub()Using Groups in re.sub()Limiting the Number of ReplacementsSyntax of re.sub()re.sub(pattern, repl, string, count=0, flags=0)Parameterspattern: The regular expression pattern we want to match.repl: The string that will replace each match.string: The string where replacements will be made.ReturnThe return type of re.sub() is a string.Using Groups in re.sub()If regular expression has capture groups(defined by parentheses()), we can use the groups in the replacement string using \1,\3,etc., or by using replacement function. Python import re a = "John 25, Jane 30, Jack 22" # Match name and age pattern = r"(\w+) (\d+)" # Use age first, then name repl = r"\2 years old, \1" # Swap names and ages result = re.sub(pattern, repl, a) print(result) Output25 years old, John, 30 years old, Jane, 22 years old, Jack Explanation:This code uses re.sub() to find all matches of a name followed by an age (e.g., "John 25") in the string and swaps the order, placing the age first followed by the name. The replacement string \2 years old, \1 uses the second capture group (age) and the first capture group (name) to format the output.Limiting the Number of ReplacementsTo limit the number of replacements in re.sub(), use the count parameter. By default, count=0, meaning all occurrences are replaced. Specifying a positive integer limits the number of replacements to that value. Python import re a = "apple orange apple banana" pattern = "apple" repl = "grape" # Replace only the first occurrence of "apple" result = re.sub(pattern, repl, a, count=1) print(result) Outputgrape orange apple banana Explanation:This code uses re.sub() to replace only the first occurrence of the word "apple" in the string a with "grape", as specified by the count=1 parameter. Subsequent occurrences of "apple" are left unchanged in the result. Comment More infoAdvertise with us Next Article re.sub() - Python RegEx P pragya22r4 Follow Improve Article Tags : Python python-regex python Practice Tags : pythonpython Similar Reads Python Tutorial | Learn Python Programming Language Python Tutorial â Python is one of the most popular programming languages. Itâs simple to use, packed with features and supported by a wide range of libraries and frameworks. 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