Python Regex (original) (raw)

A regular expression (or regex) is a sequence of characters that specifies a search pattern. In practice, you’ll find the regular expressions in many applications such as search engines, search and replace dialogs of text editors.

In Python, a regular expression is a separate programming language. It is embedded in Python. To interact with the regular expressions, you use the built-in re module:

The re module has many helpful classes and functions that help you to manage regular expressions effectively.

Section 1. Basic Regular Expressions #

This section introduces the regular expression basics including functions, character sets, anchors, and word boundaries.

Regular expressions – learn how regular expressions work in Python and how to use functions in the re module to match a string for a pattern.
Character sets – introduce to you the character sets (\d, \w, \s) that match digits, word characters, and spaces.
Anchors – show you how to use the caret (^) and dollar ($) anchors to match at the beginning and end of a string.
Word Boundary – guide you on how to use word boundary (\b) to match the whole word.

Section 2. Quantifiers #

This section shows you how to apply quantifiers to specific parts and two modes of quantifiers including greedy and lazy.

Quantifiers – learn how to use the quantifiers to match a number of instances of a character or character class.
Greedy Quantifiers – learn how the greedy quantifiers work.
Non-greedy (or lazy) Quantifiers – explain how non-greedy quantifiers works and show you how to turn greedy quantifiers into non-greedy quantifiers.

Section 3. Sets and Ranges #

This section covers the sets and ranges to match the characters.

Sets & Ranges – learn how to use the sets and ranges to match a character in a set or range of characters.

Section 4. Grouping #

This section shows you how to use the grouping to extract portions of information, reference the preceding group, and apply alternation.

Capturing groups – include a part of a match in the matches array and assign it a name using a named group.
Backreferences – learn about backreferences and how to apply them effectively.
Alternation – show you how to use the “OR” operator in regular expressions.
Non-capturing groups – create a group but don’t save it in the groups of the match.

Section 5. Look Around #

This section explains the concepts of different types of look-around mechanisms.

Lookahead – introduce to you the lookahead concept and how to use it to match X only if it is followed by Y.
Lookbehind – explain the lookbehind concept and how to match X only if there is Y before it.

Section 6. Python regex functions #

This section discusses the regular expression functions in the re module in detail and the regex flags.

findall() – find all matches that match a regular expression in a string.
fullmatch() – match the whole string with a pattern.
finditer() – return an iterator yielding Match objects over all non-overlapping matches for a regular expression in a string.
match() – check if zero or more characters at the beginning of a string match a regular expression.
search() – search for the first match in a string.
sub() – return a string with matches replaced with a replacement.
split() – split a string by the matches of a regular expression.
Regex flags – learn about the regex flags and how they change the way the regex engine matches patterns.

Section 7. Python Regex Cheat Sheet #

Regex Cheat Sheet – provide you with a Python regular expression cheat sheet.

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