Character class
A character class is a regular-expression construct that matches one character belonging to, or excluded from, a specified set, range, or property.
Tiny Python Projects: Learn coding and testing with puzzles and games
A character class is a regular-expression construct that matches one character from a specified set or range.
- How it is used
- Uses character classes to find, replace, extract, and validate constrained text with Python regular expressions.
- How deep it goes
- Explains listed characters, ranges, negation, quantifiers, anchors, and capture-group combinations through runnable examples.
- Examples
- Demonstrates vowel replacement, consonant detection, word transformation, placeholder extraction, password cleaning, and board validation.
- What you can do after
- Apply it via Python's re module to express character sets, exclude characters, and combine classes with broader patterns.
Secrets of the JavaScript Ninja, Second Edition
A regular expression construct in square brackets that matches one character from a specified set or range, optionally negated.
- How it is used
- Selects one character from a set or range when a literal character is too restrictive.
- How deep it goes
- Defines explicit, negated, and ranged classes, then works through a newline-matching idiom without an exhaustive regex treatment.
- Examples
- Uses `[abc]`, `[^abc]`, `[a-m]`, and assertions comparing `/.*/` with `/[\S\s]*/` on a string containing a newline.
- What you can do after
- Apply it via JavaScript regular expressions to choose characters from sets and match across newlines.
Read how Secrets of the JavaScript Ninja, Second Edition explains character class →
The Quick Python Book, Fourth Edition
A character class is a regular-expression construct that matches one character from a specified set or range.
- How it is used
- Selects allowable characters within Python regex patterns, including case variants and name components in contact records.
- How deep it goes
- Defines single-character matching, ranges, and literal-hyphen placement, then applies repetition; leaves broader regex subtleties to Python’s documentation.
- Examples
- Uses `[hH]ello`, letter and digit ranges, and hyphenated names in a name-and-phone-number pattern.
- What you can do after
- Apply it via Python `re` to choose permitted characters in patterns while recognizing that a broad class can match unwanted strings.
Read how The Quick Python Book, Fourth Edition explains character class →
Learn PowerShell in a Month of Lunches: Fourth Edition, Covers Windows, Linux, and macOS
A character class is a regular-expression construct that matches a character selected from, or excluded by, a specified set or range.
- How it is used
- Filters Windows event-log and text-file content by requiring characters to belong to selected categories or ranges.
- How deep it goes
- Demonstrates \w, \W, combined classes, numeric ranges, and a practical PowerShell pattern without developing regex internals.
- Examples
- Uses computer-account names in Windows security events and log lines containing mixed word, nonword, and numeric characters.
- What you can do after
- Apply it via PowerShell Select-String to locate log messages whose characters meet practical account-name or log-text constraints.
Natural Language Processing in Action, Second Edition
A regular-expression construct that matches one character from a specified set or range.
- How it is used
- Supports precise pattern-based intent recognition for commands and greetings.
- How deep it goes
- Defines ranges and repetition, then demonstrates combined classes in runnable greeting patterns without covering regex internals.
- Examples
- Uses lowercase-letter ranges, greeting strings, whitespace and punctuation classes, and captured names in Python.
- What you can do after
- Apply it via Python's re package to match character ranges and assemble greeting-recognition patterns.
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Modern C, Third Edition
A character class is a set of characters sharing a property such as being alphabetic, numeric, whitespace, or punctuation.
- How it is used
- Classifies characters for string processing, case conversion, numeric conversion, and formatted input.
- How deep it goes
- Defines common predicates, locale extensions, integer interfaces, and scan-set syntax, then demonstrates classifier-based conversion.
- Examples
- Uses ctype predicates, a hexadecimal-style converter, and scanf sets for vowels and newline-delimited input.
- What you can do after
- Apply character classes via <ctype.h> classifiers, case conversions, conversion routines, and scanf scan sets.
Modern C
A character class is a set of characters sharing a property such as being alphabetic, numeric, or whitespace.
- How it is used
- Supports encoding-independent character inspection, case conversion, string processing, numeric conversion, and formatted input.
- How deep it goes
- Defines standard classifiers, relationships, locale extensions, and scan-set syntax, but defers wider multibyte-character treatment.
- Examples
- Uses hexatridecimal conversion, vowel scanning, and whole-line scanning with a negated newline class.
- What you can do after
- Apply ctype.h classifiers and scanf scan sets to recognize, convert, and selectively read characters.
The Well-Grounded Rubyist, Fourth Edition
The word character class is the regular-expression character class matching letters, numbers, and underscore.
- How it is used
- Constrains regular-expression matches and scans word-like text without accepting every character.
- How deep it goes
- Explains explicit, ranged, negated, predefined, and POSIX classes, including single-character matching and Unicode behavior.
- Examples
- Uses rejected, hexadecimal strings, digit scans, proper names, Unicode letters, and Greek characters as matching examples.
- What you can do after
- Apply it via Ruby regular expressions to recognize constrained characters, scan word-like runs, and choose Unicode-aware alternatives.
Read how The Well-Grounded Rubyist, Fourth Edition explains character class →
Python How-To
A character class is a regular-expression shorthand or bracketed construct that matches characters sharing a specified property or membership condition.
- How it is used
- Builds regular-expression patterns that select characters by property, explicit membership, range, or exclusion.
- How deep it goes
- Explains shorthand, ranges, combinations, complements, and bracket syntax with matching output, while deferring broader pattern operators.
- Examples
- Uses [lmn], [a-z], [^a], \d, \D, \s, \S, \w, and \W against short test strings.
- What you can do after
- Apply it via regular-expression search and find-all functions to locate selected characters in strings.
Related concepts
- regular expressionpart of · A formal pattern notation that describes sets of strings and enables text to be matched, searched, extracted, or transformed.
- digitequivalent to · A digit is a symbol representing a numerical value in a positional numeral system, such as one of the symbols 0 through 9 in decimal notation.
- word characterincludes · A word character is a character that belongs to a regular expression engine’s word-character class, commonly including letters, digits, and underscores.
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