add_implicit_resolver on a subclass may affect super_class resolvers

[Alex Garel <alex.garel@…>]

Normally if I add a new implicit resolver to a subclass of a loader, super class shall not be affected.

Yet this is the case if some letter of first argument matches an existing implicit resolver in super.

>>> import yaml
>>> import re

>>> class DummyLoader(yaml.SafeLoader):
...     pass
...
>>> DummyLoader.add_implicit_resolver(u'!yeah',re.compile(ur'Yeah'),
... first='Y')  # first is the same as bool implicit resolver of SafeLoader

>>> yaml.safe_load('Yeah') # I use SafeLoader which shall ignore !yeah
Traceback (most recent call last):
...
yaml.constructor.ConstructorError: could not determine a constructor for the tag '!yeah'
  in "<string>", line 1, column 1:
    Yeah

This comes from line 26-27 of resolver.py:BaseResolver.add_implicit_resolver:

        if not 'yaml_implicit_resolvers' in cls.__dict__:
            cls.yaml_implicit_resolvers = cls.yaml_implicit_resolvers.copy()

cls.yaml_implicit_resolvers.copy() is not enough as it will keep existing lists instead of cloning them.

Instead this shall be:

from copy import copy

then:

        if not 'yaml_implicit_resolvers' in cls.__dict__:
            cls.yaml_implicit_resolvers = {}
            for k, v in cls.yaml_implicit_resolvers.items():
                cls.yaml_implicit_resolvers[k] = copy(v)