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import os
from contextlib import contextmanager
from functools import partial
from gc import get_referrers, get_referents
from operator import setitem, getitem
from types import ModuleType
from typing import Any, TypeVar, Callable, Dict, Tuple
from testfixtures.resolve import resolve, not_there, Resolved, classmethod_type, class_type
from testfixtures.utils import wrap, extend_docstring
import warnings
# Should be Literal[setattr, getattr] but Python 3.8 only.
Accessor = Callable[[Any, str], Any]
def not_same_descriptor(x, y, descriptor):
return isinstance(x, descriptor) and not isinstance(y, descriptor)
R = TypeVar('R')
class Replacer:
"""
These are used to manage the mocking out of objects so that units
of code can be tested without having to rely on their normal
dependencies.
"""
def __init__(self):
self.originals: Dict[int, Tuple[Any, Resolved]] = {}
def _replace(self, resolved: Resolved, value):
if value is not_there:
if resolved.setter is setattr:
try:
delattr(resolved.container, resolved.name)
except AttributeError:
pass
if resolved.setter is setitem:
try:
del resolved.container[resolved.name]
except KeyError:
pass
else:
resolved.setter(resolved.container, resolved.name, value)
def __call__(self, target: Any, replacement: R, strict: bool = True,
container: Any = None, accessor: Accessor = None, name: str = None) -> R:
"""
Replace the specified target with the supplied replacement.
"""
if name is None and accessor is not None:
raise TypeError('accessor is not used unless name is specified')
if isinstance(target, str):
if name is not None:
raise TypeError('name cannot be specified when target is a string')
resolved = resolve(target, container)
else:
found = not_there
if container is None:
container = target
name = name or getattr(target, '__name__', None)
if name is None:
raise TypeError('name must be specified when target is not a string')
else:
if accessor is None:
try:
accessor = getitem
found = accessor(container, name)
except KeyError:
pass
except TypeError:
accessor = getattr
found = accessor(container, name, not_there)
else:
try:
found = accessor(container, name)
except (KeyError, AttributeError):
pass
if strict and not (found is not_there or target is container):
expected = accessor(container, name)
if target is not expected:
raise AssertionError(f'{name!r} resolved to {found}, expected {target}')
resolved = Resolved(
container,
setitem if accessor is getitem else setattr,
name,
found
)
if resolved.setter is None:
raise ValueError('target must contain at least one dot!')
if resolved.found is not_there and strict:
raise AttributeError('Original %r not found' % resolved.name)
replacement_to_use = replacement
if isinstance(resolved.container, type):
# if we have a descriptor, don't accidentally use the result of its __get__ method:
if resolved.name in resolved.container.__dict__:
resolved.found = resolved.container.__dict__[resolved.name]
if not_same_descriptor(resolved.found, replacement, classmethod):
replacement_to_use = classmethod(replacement)
elif not_same_descriptor(resolved.found, replacement, staticmethod):
replacement_to_use = staticmethod(replacement)
self._replace(resolved, replacement_to_use)
key = id(target)
if key not in self.originals:
self.originals[key] = target, resolved
return replacement
def replace(self, target: Any, replacement: Any, strict: bool = True,
container: Any = None, accessor: Accessor = None, name: str = None) -> None:
"""
Replace the specified target with the supplied replacement.
"""
self(target, replacement, strict, container, accessor, name)
def in_environ(self, name: str, replacement: Any) -> None:
"""
This method provides a convenient way of ensuring an environment variable
in :any:`os.environ` is set to a particular value.
If you wish to ensure that an environment variable is *not* present,
then use :any:`not_there` as the ``replacement``.
"""
self(os.environ, name=name, accessor=getitem, strict=False,
replacement=not_there if replacement is not_there else str(replacement))
def _find_container(self, attribute, name: str, break_on_static: bool):
for referrer in get_referrers(attribute):
if break_on_static and isinstance(referrer, staticmethod):
return None, referrer
elif isinstance(referrer, dict) and '__dict__' in referrer:
if referrer.get(name) is attribute:
for container in get_referrers(referrer):
if isinstance(container, type):
return container, None
return None, None
def on_class(self, attribute: Callable, replacement: Any, name: str = None) -> None:
"""
This method provides a convenient way to replace methods, static methods and class
methods on their classes.
If the attribute being replaced has a ``__name__`` that differs from the attribute
name on the class, such as that returned by poorly implemented decorators, then
``name`` must be used to provide the correct name.
"""
if not callable(attribute):
raise TypeError('attribute must be callable')
name = name or getattr(attribute, '__name__', None)
container = None
if isinstance(attribute, classmethod_type):
for referred in get_referents(attribute):
if isinstance(referred, class_type):
container = referred
else:
container, staticmethod_ = self._find_container(attribute, name, break_on_static=True)
if staticmethod_ is not None:
container, _ = self._find_container(staticmethod_, name, break_on_static=False)
if container is None:
raise AttributeError(f'could not find container of {attribute!r} using name {name!r}')
self(container, name=name, accessor=getattr, replacement=replacement)
def in_module(self, target: Any, replacement: Any, module: ModuleType = None) -> None:
"""
This method provides a convenient way to replace targets that are module globals,
particularly functions or other objects with a ``__name__`` attribute.
If an object has been imported into a module other than the one where it has been
defined, then ``module`` should be used to specify the module where you would
like the replacement to occur.
"""
container = module or resolve(target.__module__).found
name = target.__name__
self(container, name=name, accessor=getattr, replacement=replacement)
def restore(self) -> None:
"""
Restore all the original objects that have been replaced by
calls to the :meth:`replace` method of this :class:`Replacer`.
"""
for id_, (target, original) in tuple(self.originals.items()):
self._replace(original, original.found)
del self.originals[id_]
def __enter__(self):
return self
def __exit__(self, type, value, traceback):
self.restore()
def __del__(self):
if self.originals:
# no idea why coverage misses the following statement
# it's covered by test_replace.TestReplace.test_replacer_del
warnings.warn( # pragma: no cover
'Replacer deleted without being restored, '
'originals left: %r' % {k:v for (k, v) in self.originals.values()}
)
def replace(
target: Any, replacement: Any, strict: bool = True,
container: Any = None, accessor: Accessor = None, name: str = None
) -> Callable[[Callable], Callable]:
"""
A decorator to replace a target object for the duration of a test
function.
"""
r = Replacer()
return wrap(
partial(r.__call__, target, replacement, strict, container, accessor, name),
r.restore
)
@contextmanager
def replace_in_environ(name: str, replacement: Any):
"""
This context manager provides a quick way to use :meth:`Replacer.in_environ`.
"""
with Replacer() as r:
r.in_environ(name, replacement)
yield
@contextmanager
def replace_on_class(attribute: Callable, replacement: Any, name: str = None):
"""
This context manager provides a quick way to use :meth:`Replacer.on_class`.
"""
with Replacer() as r:
r.on_class(attribute, replacement, name)
yield
@contextmanager
def replace_in_module(target: Any, replacement: Any, module: ModuleType = None):
"""
This context manager provides a quick way to use :meth:`Replacer.in_module`.
"""
with Replacer() as r:
r.in_module(target, replacement, module)
yield
class Replace(object):
"""
A context manager that uses a :class:`Replacer` to replace a single target.
"""
def __init__(
self, target: Any, replacement: R, strict: bool = True,
container: Any = None, accessor: Accessor = None, name: str = None
):
self.target = target
self.replacement = replacement
self.strict = strict
self.container: Any = container
self.accessor: Accessor = accessor
self.name: str = name
self._replacer = Replacer()
def __enter__(self) -> R:
return self._replacer(
self.target, self.replacement, self.strict, self.container, self.accessor, self.name
)
def __exit__(self, exc_type, exc_val, exc_tb):
self._replacer.restore()
replace_params_doc = """
:param target:
This must be one of the following:
- A string containing the dotted-path to the object to be replaced, in which case it will be
resolved the the object to be replaced.
This path may specify a module in a package, an attribute of a module, or any attribute of
something contained within a module.
- The container of the object to be replaced, in which case ``name`` must be specified.
- The object to be replaced, in which case ``container`` must be specified.
``name`` must also be specified if it cannot be obtained from the ``__name__`` attribute
of the object to be replaced.
:param replacement: The object to use as a replacement.
:param strict: When `True`, an exception will be raised if an
attempt is made to replace an object that does
not exist or if the object that is obtained using the ``accessor`` to
access the ``name`` from the ``container`` is not identical to the ``target``.
:param container:
The container of the object from which ``target`` can be accessed using either
:func:`getattr` or :func:`~operator.getitem`.
:param accessor:
Either :func:`getattr` or :func:`~operator.getitem`. If not supplied, this will be inferred
preferring :func:`~operator.getitem` over :func:`getattr`.
:param name:
The name used to access the ``target`` from the ``container`` using the ``accessor``.
If required but not specified, the ``__name__`` attribute of the ``target`` will be used.
"""
# add the param docs, so we only have one copy of them!
extend_docstring(replace_params_doc,
[Replacer.__call__, Replacer.replace, replace, Replace])