== Why is this an issue?

An `re.sub` call always performs an evaluation of the first argument as a regular expression, even if no regular expression features were used. This has a significant performance cost and therefore should be used with care.


When `re.sub` is used, the first argument should be a real regular expression. If it's not the case, `str.replace` does exactly the same thing as `re.sub` without the performance drawback of the regex.


This rule raises an issue for each `re.sub` used with a simple string as first argument which doesn't contains special regex character or pattern.


=== Noncompliant code example

[source,python]
----
init = "Bob is a Bird... Bob is a Plane... Bob is Superman!"
changed = re.sub(r"Bob is", "It's", init) # Noncompliant
changed = re.sub(r"\.\.\.", ";", changed) # Noncompliant
----


=== Compliant solution

[source,python]
----
init = "Bob is a Bird... Bob is a Plane... Bob is Superman!"
changed = init.replace("Bob is", "It's")
changed = changed.replace("...", ";")
----
Or, with a regex:

[source,python]
----
init = "Bob is a Bird... Bob is a Plane... Bob is Superman!"
changed = re.sub(r"\w*\sis", "It's", init)
changed = re.sub(r"\.{3}", ";", changed)
----