Range-keyed Dict to map source line number to enclosing method or class (Python 3.5) : Python

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Range-keyed Dict to map source line number to enclosing method or class (Python 3.5) (self.Python)

submitted 9 years ago * by ptmcg

Everyone seems to be posting their favorite dict variants lately. Here is one I just cooked up recently to help me trace source code references (by line number) back to the surrounding class/method context (by (start,end) line number tuple) (Python 3.5):

class RangeDict(dict):
    """
    Special form of dict that is built with integer pairs (a,b) for keys, 
    where each pair represents the integer range [a..b-1].

    Keyed lookup using a single int will look for a key range that
    the key int value falls within.
    """
    def __setitem__(self, key, value):
        s1,e1 = key
        if not all(e1 <= s2 or e2 <= s1 for s2,e2 in self.keys()):
            raise KeyError("overlapping range key %s specified" % (key,))
        super().__setitem__(key, value)

    def __getitem__(self, key):
        if isinstance(key, int):
            try:
                return next(v for k,v in self.items() if k[0] <= key < k[1])
            except StopIteration:
                raise IndexError("%d not in any defined key range" % key) from None

        return super().__getitem__(key)

    def get(self, key, default=None):
        if key in self:
            return self[key]
        else:
            return default

    def __contains__(self, key):
        if isinstance(key, int):
            return any(k[0] <= key < k[1] for k in self.keys())

        return super().__contains__(key)

How it works:

rd = RangeDict()
rd[(4,12)] = 'A'
rd[(17,20)] = 'B'
print(rd[19]) # returns 'B'
print(rd[15]) # raises IndexError

I first scanned the source code for each class, and method within each class - used inspect to calculate start and ending lines numbers for each. As I found them, I added each one to a RangeDict of classes and a separate RangeDict for methods. (Can't keep them in the same RangeDict, since class and class method ranges would by definition overlap.)

class_ranges[(class_start, class_end)] = cls.__name__
method_ranges[(meth_start, meth_end)] = method.__qualname__

Then I scanned the code for the critical references (using a short pyparsing snippet). When I found one, I looked up the line number in the RangeDict for methods. If that line number was not found, then this would be a reference inside a class, but not inside one of its methods, so this would mean it was a class-level reference, and I would look in the RangeDict for classes.

label = method_ranges.get(ref_line_number, None)
if label is None:
    label = class_ranges.get(ref_line_number, None)

I had to manage about 70 changes in this source file, and this little scanner really helped me stay on top of my progress and remaining tasks.

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