Fixed Improper Method Call: Replaced NotImplementedError

[fazledyn-or]

Details

While triaging your project, our bug fixing tool generated the following message(s)-

In file: mapcss_lib.py, class: str_value_, there is a special method __rmul__ that raises a NotImplementedError. If a special method supporting a binary operation is not implemented it should return NotImplemented. On the other hand, NotImplementedError should be raised from abstract methods inside user defined base classes to indicate that derived classes should override those methods. iCR suggested that the special method __rmul__ should return NotImplemented instead of raising an exception. An example of how NotImplemented helps the interpreter support a binary operation is here.

Related Documentation

• docs.python.org - NotImplemented
• docs.python.org - NotImplementedError
• docs.python.org - Implementing Arithmetic Operators

Moreover, we noticed that a method called __rdiv__ was defined in the same file. It is to be noted that this method belongs to Python 2.0 according to the documentation. The Python 3 equivalent of that method is __rtruediv__. In that's the case and you're willing, I can rename the __rdiv__ method to __rtruediv__.

Changes

• Replaced NotImplementedError with NotImplemented

Previously Found & Fixed

• https://www.github.com/SciTools/iris/pull/5544
• https://www.github.com/cupy/cupy/pull/7900
• https://www.github.com/ethereum/web3.py/pull/3080

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This work is done by the security researchers from OpenRefactory and is supported by the Open Source Security Foundation (OpenSSF): Project Alpha-Omega. Alpha-Omega is a project partnering with open source software project maintainers to systematically find new, as-yet-undiscovered vulnerabilities in open source code - and get them fixed – to improve global software supply chain security.

The bug is found by running the Intelligent Code Repair (iCR) tool by OpenRefactory and then manually triaging the results.

[frodrigo]

To be checked if using return in place of exception does not have any side effect.

[Famlam]

I tested it with the following code, which obviously should fail as you cannot subtract "8" from a string.

node[x][tag("a")-tag("b")="hello"] {
  throwWarning: "x";
  assertNoMatch: "node a=test b=8 x=abc";
}

Compilation of the mapcss code works in either case (the minus is not evaluated during compiling)

Running the code with raise fails at the position of raise and isn't caught

plugins/test.py:31: in node
    try: match = ((mapcss._tag_capture(capture_tags, 0, tags, 'x')) and (mapcss.tag(tags, 'a')-mapcss.tag(tags, 'b') == 'hello'))
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = 'test', o = '8'

    def __sub__(self, o):
        if self.none:
            return None_value
        elif o.__class__ == int:
            return str_value(self.to_n() - o)
        else:
>           raise NotImplementedError
E           NotImplementedError

modules/mapcss_lib.py:72: NotImplementedError

Running the code with return NotImplemented fails at the code point where the minus is evaluated:

self = <plugins.test.test object at 0x7f78ebf72c50>, data = {'id': 0, 'lat': 0, 'lon': 0}
tags = {'a': 'test', 'b': '8', 'x': 'abc'}

    def node(self, data, tags):
        capture_tags = {}
        keys = tags.keys()
        err = []


        # node[x][tag("a")-tag("b")="hello"]
        if ('x' in keys):
            match = False
            if not match:
                capture_tags = {}
>               try: match = ((mapcss._tag_capture(capture_tags, 0, tags, 'x')) and (mapcss.tag(tags, 'a')-mapcss.tag(tags, 'b') == 'hello'))
E               TypeError: unsupported operand type(s) for -: 'str_value_' and 'str_value_'

plugins/test.py:31: TypeError

I don't have a clear favorite out of the two, but it indeed seems that Python advocates the return option. It would differ in case we're evaluating an operator with a str_value_-type with a non-str_value_-type where the arithmetic operators are defined differently, but I can't think of a test case for this. For example, in the following case (string minus number) the behavior is the same with raise or return (a silent "no match"):

node[x][tag("a")-number_of_tags()="hello"] {
  throwWarning: "x";
  assertNoMatch: "node a=test b=8 x=abc";
}

---

Moreover, we noticed that a method called rdiv was defined in the same file. It is to be noted that this method belongs to Python 2.0 according to the documentation. The Python 3 equivalent of that method is rtruediv. In that's the case and you're willing, I can rename the rdiv method to rtruediv.

Seems to be correct based on the documentation (same for __div__ vs __truediv__, but that was already done prior) although I don't know any cases where mapcss uses this function actually.

[frodrigo]

Ok thank you a lot for looking into this.

Seems to be correct based on the documentation (same for div vs truediv, but that was already done prior) although I don't know any cases where mapcss uses this function actually.

Probably forgotten here from the py2 -> py3 migration. I think the method could be removed.

[fazledyn-or]

@frodrigo @Famlam thanks for the detailed explanation.
So, should I go and remove the __rdiv__ method?

[frodrigo]

It looks like __rdiv__ should be __rtruediv__ in py3.

[Famlam]

Correct, the question is mostly whether we want to remove it (since apparently it's never called) or rename it. I'm fine with it either way. I think you mean your preference is to rename it?

[fazledyn-or]

In mapcss_lib.py file, I can see that the implementation of __truediv__ is similar to __rdiv__. I think it'd be best to just renamed __rdiv__ to __rtruediv__.

[frodrigo]

Merged. Thank you.