""" monkeypatching and mocking functionality. """
from __future__ import absolute_import, division, print_function
import os
import sys
import re
from contextlib import contextmanager
import six
from _pytest.fixtures import fixture
RE_IMPORT_ERROR_NAME = re.compile("^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 %s: %s" % (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 %s has no attribute %r" % (type(obj).__name__, ann, name)
)
return obj
def derive_importpath(import_path, raising):
if not isinstance(import_path, six.string_types) or "." not in import_path:
raise TypeError("must be absolute import path string, not %r" % (import_path,))
module, attr = import_path.rsplit(".", 1)
target = resolve(module)
if raising:
annotated_getattr(target, attr, ann=module)
return attr, target
class Notset(object):
def __repr__(self):
return "<notset>"
notset = Notset()
[docs]class MonkeyPatch(object):
""" 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):
"""
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 <https://github.com/pytest-dev/pytest/issues/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, six.string_types):
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" % (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
if name is notset:
if not isinstance(target, six.string_types):
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:
self._setattr.append((target, name, getattr(target, name, notset)))
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."""
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 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. """
if self._savesyspath is None:
self._savesyspath = sys.path[:]
sys.path.insert(0, str(path))
[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()
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