Source code for _pytest.monkeypatch

"""Monkeypatching and mocking functionality."""
import os
import re
import sys
import warnings
from contextlib import contextmanager
from typing import Any
from typing import Generator
from typing import List
from typing import MutableMapping
from typing import Optional
from typing import overload
from typing import Tuple
from typing import TypeVar
from typing import Union

from _pytest.compat import final
from _pytest.fixtures import fixture
from _pytest.warning_types import PytestWarning

RE_IMPORT_ERROR_NAME = re.compile(r"^No module named (.*)$")

K = TypeVar("K")
V = TypeVar("V")

[docs]@fixture def monkeypatch() -> Generator["MonkeyPatch", None, None]: """A convenient fixture for monkey-patching. The fixture provides these methods to modify objects, dictionaries, or :data:`os.environ`: * :meth:`monkeypatch.setattr(obj, name, value, raising=True) <pytest.MonkeyPatch.setattr>` * :meth:`monkeypatch.delattr(obj, name, raising=True) <pytest.MonkeyPatch.delattr>` * :meth:`monkeypatch.setitem(mapping, name, value) <pytest.MonkeyPatch.setitem>` * :meth:`monkeypatch.delitem(obj, name, raising=True) <pytest.MonkeyPatch.delitem>` * :meth:`monkeypatch.setenv(name, value, prepend=None) <pytest.MonkeyPatch.setenv>` * :meth:`monkeypatch.delenv(name, raising=True) <pytest.MonkeyPatch.delenv>` * :meth:`monkeypatch.syspath_prepend(path) <pytest.MonkeyPatch.syspath_prepend>` * :meth:`monkeypatch.chdir(path) <pytest.MonkeyPatch.chdir>` * :meth:`monkeypatch.context() <pytest.MonkeyPatch.context>` All modifications will be undone after the requesting test function or fixture has finished. The ``raising`` parameter determines if a :class:`KeyError` or :class:`AttributeError` will be raised if the set/deletion operation does not have the specified target. To undo modifications done by the fixture in a contained scope, use :meth:`context() <pytest.MonkeyPatch.context>`. """ mpatch = MonkeyPatch() yield mpatch mpatch.undo()
def resolve(name: str) -> object: # Simplified from zope.dottedname. parts = name.split(".") used = parts.pop(0) found: object = __import__(used) for part in parts: used += "." + part try: found = getattr(found, part) except AttributeError: pass else: continue # We use explicit un-nesting of the handling block in order # to avoid nested exceptions. try: __import__(used) except ImportError as ex: expected = str(ex).split()[-1] if expected == used: raise else: raise ImportError(f"import error in {used}: {ex}") from ex found = annotated_getattr(found, part, used) return found def annotated_getattr(obj: object, name: str, ann: str) -> object: try: obj = getattr(obj, name) except AttributeError as e: raise AttributeError( "{!r} object at {} has no attribute {!r}".format( type(obj).__name__, ann, name ) ) from e return obj def derive_importpath(import_path: str, raising: bool) -> Tuple[str, object]: if not isinstance(import_path, str) or "." not in import_path: raise TypeError(f"must be absolute import path string, not {import_path!r}") module, attr = import_path.rsplit(".", 1) target = resolve(module) if raising: annotated_getattr(target, attr, ann=module) return attr, target class Notset: def __repr__(self) -> str: return "<notset>" notset = Notset()
[docs]@final class MonkeyPatch: """Helper to conveniently monkeypatch attributes/items/environment variables/syspath. Returned by the :fixture:`monkeypatch` fixture. :versionchanged:: 6.2 Can now also be used directly as `pytest.MonkeyPatch()`, for when the fixture is not available. In this case, use :meth:`with MonkeyPatch.context() as mp: <context>` or remember to call :meth:`undo` explicitly. """ def __init__(self) -> None: self._setattr: List[Tuple[object, str, object]] = [] self._setitem: List[Tuple[MutableMapping[Any, Any], object, object]] = [] self._cwd: Optional[str] = None self._savesyspath: Optional[List[str]] = None
[docs] @classmethod @contextmanager def context(cls) -> Generator["MonkeyPatch", None, None]: """Context manager that returns a new :class:`MonkeyPatch` object which undoes any patching done inside the ``with`` block upon exit. Example: .. code-block:: python import functools def test_partial(monkeypatch): with monkeypatch.context() as m: m.setattr(functools, "partial", 3) Useful in situations where it is desired to undo some patches before the test ends, such as mocking ``stdlib`` functions that might break pytest itself if mocked (for examples of this see :issue:`3290`). """ m = cls() try: yield m finally: m.undo()
@overload def setattr( self, target: str, name: object, value: Notset = ..., raising: bool = ..., ) -> None: ... @overload def setattr( self, target: object, name: str, value: object, raising: bool = ..., ) -> None: ...
[docs] def setattr( self, target: Union[str, object], name: Union[object, str], value: object = notset, raising: bool = True, ) -> None: """ Set attribute value on target, memorizing the old value. For example: .. code-block:: python import os monkeypatch.setattr(os, "getcwd", lambda: "/") The code above replaces the :func:`os.getcwd` function by a ``lambda`` which always returns ``"/"``. For convenience, you can specify a string as ``target`` which will be interpreted as a dotted import path, with the last part being the attribute name: .. code-block:: python monkeypatch.setattr("os.getcwd", lambda: "/") Raises :class:`AttributeError` if the attribute does not exist, unless ``raising`` is set to False. **Where to patch** ``monkeypatch.setattr`` works by (temporarily) changing the object that a name points to with another one. There can be many names pointing to any individual object, so for patching to work you must ensure that you patch the name used by the system under test. See the section :ref:`Where to patch <python:where-to-patch>` in the :mod:`unittest.mock` docs for a complete explanation, which is meant for :func:`unittest.mock.patch` but applies to ``monkeypatch.setattr`` as well. """ __tracebackhide__ = True import inspect if isinstance(value, Notset): if not isinstance(target, str): raise TypeError( "use setattr(target, name, value) or " "setattr(target, value) with target being a dotted " "import string" ) value = name name, target = derive_importpath(target, raising) else: if not isinstance(name, str): raise TypeError( "use setattr(target, name, value) with name being a string or " "setattr(target, value) with target being a dotted " "import string" ) oldval = getattr(target, name, notset) if raising and oldval is notset: raise AttributeError(f"{target!r} has no attribute {name!r}") # avoid class descriptors like staticmethod/classmethod if inspect.isclass(target): oldval = target.__dict__.get(name, notset) self._setattr.append((target, name, oldval)) setattr(target, name, value)
[docs] def delattr( self, target: Union[object, str], name: Union[str, Notset] = notset, raising: bool = True, ) -> None: """Delete attribute ``name`` from ``target``. If no ``name`` is specified and ``target`` is a string it will be interpreted as a dotted import path with the last part being the attribute name. Raises AttributeError it the attribute does not exist, unless ``raising`` is set to False. """ __tracebackhide__ = True import inspect if isinstance(name, Notset): if not isinstance(target, str): raise TypeError( "use delattr(target, name) or " "delattr(target) with target being a dotted " "import string" ) name, target = derive_importpath(target, raising) if not hasattr(target, name): if raising: raise AttributeError(name) else: oldval = getattr(target, name, notset) # Avoid class descriptors like staticmethod/classmethod. if inspect.isclass(target): oldval = target.__dict__.get(name, notset) self._setattr.append((target, name, oldval)) delattr(target, name)
[docs] def setitem(self, dic: MutableMapping[K, V], name: K, value: V) -> None: """Set dictionary entry ``name`` to value.""" self._setitem.append((dic, name, dic.get(name, notset))) dic[name] = value
[docs] def delitem(self, dic: MutableMapping[K, V], name: K, raising: bool = True) -> None: """Delete ``name`` from dict. Raises ``KeyError`` if it doesn't exist, unless ``raising`` is set to False. """ if name not in dic: if raising: raise KeyError(name) else: self._setitem.append((dic, name, dic.get(name, notset))) del dic[name]
[docs] def setenv(self, name: str, value: str, prepend: Optional[str] = None) -> None: """Set environment variable ``name`` to ``value``. If ``prepend`` is a character, read the current environment variable value and prepend the ``value`` adjoined with the ``prepend`` character. """ if not isinstance(value, str): warnings.warn( # type: ignore[unreachable] PytestWarning( "Value of environment variable {name} type should be str, but got " "{value!r} (type: {type}); converted to str implicitly".format( name=name, value=value, type=type(value).__name__ ) ), stacklevel=2, ) value = str(value) if prepend and name in os.environ: value = value + prepend + os.environ[name] self.setitem(os.environ, name, value)
[docs] def delenv(self, name: str, raising: bool = True) -> None: """Delete ``name`` from the environment. Raises ``KeyError`` if it does not exist, unless ``raising`` is set to False. """ environ: MutableMapping[str, str] = os.environ self.delitem(environ, name, raising=raising)
[docs] def syspath_prepend(self, path) -> None: """Prepend ``path`` to ``sys.path`` list of import locations.""" if self._savesyspath is None: self._savesyspath = sys.path[:] sys.path.insert(0, str(path)) # # this is only needed when pkg_resources was already loaded by the namespace package if "pkg_resources" in sys.modules: from pkg_resources import fixup_namespace_packages fixup_namespace_packages(str(path)) # A call to syspathinsert() usually means that the caller wants to # import some dynamically created files, thus with python3 we # invalidate its import caches. # This is especially important when any namespace package is in use, # since then the mtime based FileFinder cache (that gets created in # this case already) gets not invalidated when writing the new files # quickly afterwards. from importlib import invalidate_caches invalidate_caches()
[docs] def chdir(self, path: Union[str, "os.PathLike[str]"]) -> None: """Change the current working directory to the specified path. Path can be a string or a path object. """ if self._cwd is None: self._cwd = os.getcwd() os.chdir(path)
[docs] def undo(self) -> None: """Undo previous changes. This call consumes the undo stack. Calling it a second time has no effect unless you do more monkeypatching after the undo call. There is generally no need to call `undo()`, since it is called automatically during tear-down. .. note:: The same `monkeypatch` fixture is used across a single test function invocation. If `monkeypatch` is used both by the test function itself and one of the test fixtures, calling `undo()` will undo all of the changes made in both functions. Prefer to use :meth:`context() <pytest.MonkeyPatch.context>` instead. """ for obj, name, value in reversed(self._setattr): if value is not notset: setattr(obj, name, value) else: delattr(obj, name) self._setattr[:] = [] for dictionary, key, value in reversed(self._setitem): if value is notset: try: del dictionary[key] except KeyError: pass # Was already deleted, so we have the desired state. else: dictionary[key] = value self._setitem[:] = [] if self._savesyspath is not None: sys.path[:] = self._savesyspath self._savesyspath = None if self._cwd is not None: os.chdir(self._cwd) self._cwd = None