A regular expression is a sequence of characters that specifies a match pattern in text. Among the most important concepts are:
- Character classes: defines a set of characters, any one of which can occur in an input string for a match to succeed.
- Quantifiers: used to specify how many instances of a character, group, or character class must be present in the input for a match.
- Wildcard (
.): matches all characters except line terminators (also matches them if the s flag is set).
Many of these features include shortcuts of widely used expressions, so there is more than one way to construct a regular expression to achieve the
same results. For example, to match a two-digit number, one could write [0-9]{2,2} or \d{2}. The latter is not only shorter
but easier to read and thus to maintain.
This rule recommends replacing some quantifiers and character classes with more concise equivalents:
-
\d for [0-9] and \D for [^0-9]
-
\w for [A-Za-z0-9_] and \W for [^A-Za-z0-9_]
-
. for character classes matching everything (e.g. [\w\W], [\d\D], or [\s\S] with
s flag)
-
x? for x{0,1}, x* for x{0,}, x+ for x{1,}, x{N} for
x{N,N}
r"[0-9]" # Noncompliant - same as r"\d"
r"[^0-9]" # Noncompliant - same as r"\D"
r"[A-Za-z0-9_]" # Noncompliant - same as r"\w"
r"[\w\W]" # Noncompliant - same as r"."
r"a{0,}" # Noncompliant - same as r"a*"
Use the more concise version to make the regex expression more readable.
r"\d"
r"\D"
r"\w"
r"."
r"a*"
