Source code for _pytest.monkeypatch

""" monkeypatching and mocking functionality.  """
import os
import re
import sys
import warnings
from contextlib import contextmanager
from typing import Generator

import pytest
from _pytest.fixtures import fixture
from _pytest.pathlib import Path

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

[docs]@fixture def monkeypatch(): """The returned ``monkeypatch`` fixture provides these helper methods to modify objects, dictionaries or os.environ:: monkeypatch.setattr(obj, name, value, raising=True) monkeypatch.delattr(obj, name, raising=True) monkeypatch.setitem(mapping, name, value) monkeypatch.delitem(obj, name, raising=True) monkeypatch.setenv(name, value, prepend=False) monkeypatch.delenv(name, raising=True) monkeypatch.syspath_prepend(path) monkeypatch.chdir(path) All modifications will be undone after the requesting test function or fixture has finished. The ``raising`` parameter determines if a KeyError or AttributeError will be raised if the set/deletion operation has no target. """ mpatch = MonkeyPatch() yield mpatch mpatch.undo()
def resolve(name): # simplified from zope.dottedname parts = name.split(".") used = parts.pop(0) found = __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 on python 3 try: __import__(used) except ImportError as ex: # str is used for py2 vs py3 expected = str(ex).split()[-1] if expected == used: raise else: raise ImportError("import error in {}: {}".format(used, ex)) found = annotated_getattr(found, part, used) return found def annotated_getattr(obj, name, ann): try: obj = getattr(obj, name) except AttributeError: raise AttributeError( "{!r} object at {} has no attribute {!r}".format( type(obj).__name__, ann, name ) ) return obj def derive_importpath(import_path, raising): if not isinstance(import_path, str) or "." not in import_path: raise TypeError( "must be absolute import path string, not {!r}".format(import_path) ) 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): return "<notset>" notset = Notset()
[docs]class MonkeyPatch: """ Object returned by the ``monkeypatch`` fixture keeping a record of setattr/item/env/syspath changes. """ def __init__(self): self._setattr = [] self._setitem = [] self._cwd = None self._savesyspath = None
[docs] @contextmanager def context(self) -> Generator["MonkeyPatch", None, None]: """ Context manager that returns a new :class:`MonkeyPatch` object which undoes any patching done inside the ``with`` block upon exit: .. 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 `#3290 <>`_. """ m = MonkeyPatch() try: yield m finally: m.undo()
[docs] def setattr(self, target, name, value=notset, raising=True): """ Set attribute value on target, memorizing the old value. By default raise AttributeError if the attribute did not exist. 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. Example: ``monkeypatch.setattr("os.getcwd", lambda: "/")`` would set the ``getcwd`` function of the ``os`` module. The ``raising`` value determines if the setattr should fail if the attribute is not already present (defaults to True which means it will raise). """ __tracebackhide__ = True import inspect if value is 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) oldval = getattr(target, name, notset) if raising and oldval is notset: raise AttributeError("{!r} has no attribute {!r}".format(target, name)) # 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, name=notset, raising=True): """ Delete attribute ``name`` from ``target``, by default raise AttributeError it the attribute did not previously exist. 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. If ``raising`` is set to False, no exception will be raised if the attribute is missing. """ __tracebackhide__ = True import inspect if name is 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, name, value): """ Set dictionary entry ``name`` to value. """ self._setitem.append((dic, name, dic.get(name, notset))) dic[name] = value
[docs] def delitem(self, dic, name, raising=True): """ Delete ``name`` from dict. Raise KeyError if it doesn't exist. If ``raising`` is set to False, no exception will be raised if the key is missing. """ 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, value, prepend=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( pytest.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, raising=True): """ Delete ``name`` from the environment. Raise KeyError if it does not exist. If ``raising`` is set to False, no exception will be raised if the environment variable is missing. """ self.delitem(os.environ, name, raising=raising)
[docs] def syspath_prepend(self, path): """ Prepend ``path`` to ``sys.path`` list of import locations. """ from pkg_resources import fixup_namespace_packages if self._savesyspath is None: self._savesyspath = sys.path[:] sys.path.insert(0, str(path)) # 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): """ Change the current working directory to the specified path. Path can be a string or a py.path.local object. """ if self._cwd is None: self._cwd = os.getcwd() if hasattr(path, "chdir"): path.chdir() elif isinstance(path, Path): # modern python uses the fspath protocol here LEGACY os.chdir(str(path)) else: os.chdir(path)
[docs] def undo(self): """ 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 that 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. """ 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, name, value in reversed(self._setitem): if value is notset: try: del dictionary[name] except KeyError: pass # was already deleted, so we have the desired state else: dictionary[name] = 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