Introduction

Python makes regular expressions available through the re module.

Regular expressions are combinations of characters that are interpreted as rules for matching substrings. For instance, the expression 'amount\\D+\\d+' will match any string composed by the word amount plus an integral number, separated by one or more non-digits, such as: amount=100, amount is 3, amount is equal to: 33, etc.

Syntax of Direct Regular Expressions

• re.match(pattern, string, flag=0) # Out: match pattern at the beginning of string or None
• re.search(pattern, string, flag=0) # Out: match pattern inside string or None
• re.findall(pattern, string, flag=0) # Out: list of all matches of pattern in string or []
• re.finditer(pattern, string, flag=0) # Out: same as re.findall, but returns iterator object
• re.sub(pattern, replacement, string, flag=0) # Out: string with replacement (string or function) in place of pattern

Syntax of Precompiled Regular Expressions

• precompiled_pattern = re.compile(pattern, flag=0)
• precompiled_pattern.match(string) # Out: match at the beginning of string or None
• precompiled_pattern.search(string) # Out: match anywhere in string or None
• precompiled_pattern.findall(string) # Out: list of all matching substrings
• precompiled_pattern.sub(string/pattern/function, string) # Out: replaced string