pytorch/torch/backends/__init__.py

from contextlib import contextmanager
import types
# The idea for this parameter is that we forbid bare assignment
# to torch.backends.<cudnn|mkldnn>.enabled and friends when running our
# test suite, where it's very easy to forget to undo the change
# later.
__allow_nonbracketed_mutation_flag = True

def disable_global_flags():
    global __allow_nonbracketed_mutation_flag
    __allow_nonbracketed_mutation_flag = False

def flags_frozen():
    return not __allow_nonbracketed_mutation_flag

@contextmanager
def __allow_nonbracketed_mutation():
    global __allow_nonbracketed_mutation_flag
    old = __allow_nonbracketed_mutation_flag
    __allow_nonbracketed_mutation_flag = True
    try:
        yield
    finally:
        __allow_nonbracketed_mutation_flag = old

class ContextProp(object):
    def __init__(self, getter, setter):
        self.getter = getter
        self.setter = setter

    def __get__(self, obj, objtype):
        return self.getter()

    def __set__(self, obj, val):
        if not flags_frozen():
            self.setter(val)
        else:
            raise RuntimeError("not allowed to set %s flags "
                               "after disable_global_flags; please use flags() context manager instead" % obj.__name__)

class PropModule(types.ModuleType):
    def __init__(self, m, name):
        super(PropModule, self).__init__(name)
        self.m = m

    def __getattr__(self, attr):
        return self.m.__getattribute__(attr)