Raw string literal

As explained in Natural Language Processing in Action, Second Edition

A Python string literal in which backslashes are preserved rather than normally interpreted as escape sequences.

>>> r = r"[^a-z]*([y]o|[h']?ello|ok|hey|(good[ ])(morn[gin']{0,3}|"
>>> r += r"afternoon|even[gin']{0,3}))[\s,;:]{1,3}([a-z]{1,20})"
>>> re_greeting = re.compile(r, flags=re.IGNORECASE)    #1
>>> re_greeting.match('Hello Rosa')
<re.Match object; span=(0, 10), match='Hello Rosa'>
>>> re_greeting.match('Hello Rosa').groups()
('Hello', None, None, 'Rosa')
>>> re_greeting.match("Good morning Rosa")
<re.Match object; span=(0, 17), match="Good morning Rosa">
>>> re_greeting.match("Good Manning Rosa")                  #2
>>> re_greeting.match('Good evening Rosa Parks').groups()    #3
('Good evening', 'Good ', 'evening', 'Rosa')
>>> re_greeting.match("Good Morn'n Rosa")
<re.Match object; span=(0, 16), match="Good Morn'n Rosa">
>>> re_greeting.match("yo Rosa")
<re.Match object; span=(0, 7), match='yo Rosa'>

How Natural Language Processing in Action, Second Edition covers it

How deep it goes

Defines backslash preservation and contrasts raw patterns with doubled escapes, without detailing string-parser internals.

Examples

Uses whitespace matching, literal curly braces, greeting patterns, and compiled regular expressions as examples.

What it assumes

Assumes basic Python strings and regular expressions while clarifying escape handling from the immediate examples.

What you can do after

Apply raw string literals to write more readable Python regular-expression patterns with unmodified backslashes.

How it connects

Connects raw string literals to regular expressions, escape sequences, character classes, and the re package.

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Also explained in

• 

  liveBookmanning.com
  The Quick Python Book, Fourth EditionA raw string literal is a Python string literal in which backslashes are generally treated as literal characters rather than introducing escape sequences.
• 

  liveBookmanning.com
  100 C++ Mistakes and How to Avoid ThemA raw string is a C++ string literal whose contents are written without interpreting ordinary escape sequences.

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Related concepts

• string literalkind of · A string literal is source-code notation that directly represents a string value.
• stringkind of · A string is a programming-language value representing an ordered sequence of characters or character units as text.
• regular expressionuses · A formal pattern notation that describes sets of strings and enables text to be matched, searched, extracted, or transformed.
• escape sequencecontrasts with · An escape sequence is source notation, typically using an escape marker, that represents a character or control value or changes how characters are interpreted.
• newlinecontrasts with · A newline is a character or character sequence that marks the boundary between consecutive lines of text.
• f-stringcontrasts with · An f-string is a Python formatted string literal that evaluates embedded expressions and inserts their formatted values into the resulting string.

This explainer was generated by Manning's knowledge graph from the text of Natural Language Processing in Action, Second Edition. The section links point to the parts of the book it draws on.