RegexValidator pattern is optional and should be required

[David Fischer]

While working on ticket #13341, I noticed that the code for RegexValidator could use a slight cleanup. Specifically, the first parameter of RegexValidator -- the regex pattern -- is optional. However, if it is not provided, a TypeError is thrown because the default value of None is passed to re.compile. The regex pattern should be required.

[David Fischer]

switched regex parameter to be required

[David Fischer]

I switched the regex parameter to required to match the ​documentation. While running the unit tests (forms & validation), I noticed that URLValidator relied on the fact that the regex parameter was optional by having a regex instance variable. I corrected that. However, this brings up a potential backwards compatibility issue.

The issue with this patch is that anybody who subclassed RegexValidator and relied on regex to be optional will have to update their code. However, it should be pretty obvious what went wrong and they probably should not have done that in the first place. I'm not sure how strict to be on maintaining backwards compatibility, but I think that breaking it in this small way will result in the cleanest code.

[Rolando Espinoza La fuente]

I just face this bug when subclassing RegexValidator. I think using self.regex instead regex as re.compile's parameter works and keeps backward compatilibity. Though, using RegexValidator without regex parameter will work in the same way that re.compile("") works.

django/core/validators.py

@@ -29 +29 @@
             self.code = code
 
         if isinstance(self.regex, basestring):
-            self.regex = re.compile(regex)
+            self.regex = re.compile(self.regex)
 
     def __call__(self, value):
         """

[David Fischer]

@darkrho

That looks like it will work and it is better than what I had attached. It passes the unit test suite (validators) and it allows you to subclass RegexValidator. As you mentioned, creating a RegexValidator without specifying the "regex" will function the same as if the empty string was passed (a RegexValidator that always matches). I think that is fine, but maybe it needs to be communicated in the docs. The docs currently specify that "regex" is not optional. It can either be left like it is because a RegexValidator that matches everything is pretty useless, but perhaps the docs should just say that by default it matches everything.

[David Fischer]

Patch leaves "regex" as optional, but documents and tests functionality

[David Fischer]

I added a patch based on darkrho's suggestion. It will not break backward compatibility with subclasses of RegexValidator. I added a note in the docs that if the user does not specify any regex, then RegexValidator will match any passed string.

[Chris Beaven]

In [16351]:

Fixes #13511 -- make regex parameter to RegexValidator to be optional. Also tidies up related docs (parameters aren't attributes). Thanks for the patch work, davidfischer.