Fixed #12914 -- Use yaml faster C implementation when available

from django.core.serializers.python import Deserializer as PythonDeserializer

from django.utils import six

# Use the C (faster) implementation if possible

try:

    from yaml import CSafeLoader as SafeLoader

    from yaml import CSafeDumper as SafeDumper

except ImportError:

    from yaml import SafeLoader, SafeDumper

class DjangoSafeDumper(yaml.SafeDumper):

class DjangoSafeDumper(SafeDumper):

    def represent_decimal(self, data):

        return self.represent_scalar('tag:yaml.org,2002:str', str(data))

    else:

        stream = stream_or_string

    try:

        for obj in PythonDeserializer(yaml.safe_load(stream), **options):

        for obj in PythonDeserializer(yaml.load(stream, Loader=SafeLoader), **options):

            yield obj

    except GeneratorExit:

        raise