Regex Python3

Character Sets in Regular Expressions

• Regular expression character sets denoted by a pair of brackets [] will match any of the characters included within the brackets.

• For example, the regular expression con[sc]en[sc]us will match any of the spellings consensus, concensus, consencus, and concencus.

Optional Quantifiers in Regular Expressions

• In Regular expressions, optional quantifiers are denoted by a question mark ?.

• It indicates that a character can appear either 0 or 1 time.

• For example, the regular expression humou?r will match the text humour as well as the text humor.

Literals in Regular Expressions

• In Regular expression, the literals are the simplest characters that will match the exact text of the literals.

• For example, the regex monkey will completely match the text monkey but will also match monkey in text The monkeys like to eat bananas.

Fixed Quantifiers in Regular Expressions

• In Regular expressions, fixed quantifiers are denoted by curly braces {}.

• It contains either the exact quantity or the quantity range of characters to be matched.

• For example, the regular expression roa{3}r will match the text roaaar, while the regular expression roa{3,6}r will match roaaar, roaaaar, roaaaaar, or roaaaaaar.

Alternation in Regular Expressions

• Alternation indicated by the pipe symbol |, allows for the matching of either of two subexpressions.

• For example, the regex baboons|gorillas will match the text baboons as well as the text gorillas.

Anchors in Regular Expressions

• Anchors (hat ^ and dollar sign $) are used in regular expressions to match text at the start and end of a string, respectively.

• For example, the regex ^Monkeys: my mortal enemy$ will completely match the text Monkeys: my mortal enemy but not match Spider Monkeys: my mortal enemy or Monkeys: my mortal enemy in the wild.

• The ^ ensures that the matched text begins with Monkeys, and the $ ensures the matched text ends with enemy.

Regular Expressions

• Regular expressions are sequence of characters defining a pattern of text that needs to be found.

• They can be used for parsing the text files for specific pattern, verifying test results, and finding keywords in emails or webpages.

Wildcards in Regular expressions

• In Regular expression, wildcards are denoted with the period . and it can match any single character (letter, number, symbol or whitespace) in a piece of text.

• For example, the regular expression ......... will match the text orangutan, marsupial, or any other 9-character text.

Regular Expression Ranges

• Regular expression ranges are used to specify a range of characters that can be matched.

• Common regular expression ranges include: [A-Z]. : match any uppercase letter [a-z]. : match any lowercase letter [0-9]. : match any digit [A-Za-z] : match any uppercase or lowercase letter.

Shorthand Character Classes in Regular Expressions

• Shorthand character classes simplify writing regular expressions. For example, \w represents the regex range [A-Za-z0-9_], \d represents [0-9], \W represents [^A-Za-z0-9_] matching any character not included by \w, \D represents [^0-9] matching any character not included by \d.

Kleene Star & Kleene Plus in Regular Expressions

• In Regular expressions, the Kleene star(*) indicates that the preceding character can occur 0 or more times.

• For example, meo*w will match mew, meow, meooow, and meoooooooooooow.

• The Kleene plus(+) indicates that the preceding character can occur 1 or more times.

• For example, meo+w will match meow, meooow, and meoooooooooooow, but not match mew.

Grouping in Regular Expressions

• In Regular expressions, grouping is accomplished by open ( and close parenthesis ).

• Thus the regular expression I love (baboons|gorillas) will match the text I love baboons as well as I love gorillas, as the grouping limits the reach of the | to the text within the parentheses.

Credit for This Page:

https://www.codecademy.com/learn/paths/build-chatbots-with-python/tracks/rule-based-chatbots/modules/intro-to-regex/cheatsheet