Why is this an issue?
When a reluctant (or lazy) quantifier is followed by a pattern that can match the empty string or directly by the end of the regex, it will always
match zero times for
*? or one time for
+?. If a reluctant quantifier is followed directly by the end anchor
$), it behaves indistinguishably from a greedy quantifier while being less efficient.
This is likely a sign that the regex does not work as intended.
Noncompliant code example
re.replace(r"start\w*?(end)?", "x", "start123endstart456") # Noncompliant. In contrast to what one would expect, the result is not "xx"
re.match(r"^\d*?$", "123456789") # Noncompliant. Matches the same as "/^\d*$/", but will backtrack in every position.
re.replace(r"start\w*?(end|$)", "x", "start123endstart456") # Result is "xx"