Alternation is used to match a single regular expression out of several possible regular expressions. If one of the alternatives is empty it would
match any input, which is most probably a mistake.
Noncompliant code example
re.search(r"Jack|Peter|", "John") # Noncompliant - will match an empty string
re.search(r"Jack||Peter", "John") # Noncompliant - will match an empty string
Compliant solution
re.search(r"Jack|Peter", "John") # returns false
Exceptions
One could use an empty alternation to make a regular expression group optional. Rule will not report on such cases.
re.search(r"mandatory(-optional|)", "mandatory")
re.search(r"mandatory(-optional|)", "mandatory-optional")
However, if there is a quantifier after the group the issue will be reported as using both | and quantifier is redundant.
re.search(r"mandatory(-optional|)?", "mandatory-optional") # Noncompliant - using both `|` inside the group and `?` for the group.
