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patch.py
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260 lines (198 loc) Β· 7.85 KB
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import functools
import inspect
import types
from collections.abc import Callable
from typing import Any
def get_defining_object(method):
"""Returns either the class or the module that defines the given function/method."""
# adapted from https://stackoverflow.com/a/25959545/804840
if inspect.ismethod(method):
return method.__self__
if inspect.isfunction(method):
class_name = method.__qualname__.split(".<locals>", 1)[0].rsplit(".", 1)[0]
try:
# method is not bound but referenced by a class, like MyClass.mymethod
cls = getattr(inspect.getmodule(method), class_name)
except AttributeError:
cls = method.__globals__.get(class_name)
if isinstance(cls, type):
return cls
# method is a module-level function
return inspect.getmodule(method)
def to_metadata_string(obj: Any) -> str:
"""
Creates a string that helps humans understand where the given object comes from. Examples::
to_metadata_string(func_thread.run) == "function(localstack.utils.threads:FuncThread.run)"
:param obj: a class, module, method, function or object
:return: a string representing the objects origin
"""
if inspect.isclass(obj):
return f"class({obj.__module__}:{obj.__name__})"
if inspect.ismodule(obj):
return f"module({obj.__name__})"
if inspect.ismethod(obj):
return f"method({obj.__module__}:{obj.__qualname__})"
if inspect.isfunction(obj):
# TODO: distinguish bound method
return f"function({obj.__module__}:{obj.__qualname__})"
if isinstance(obj, object):
return f"object({obj.__module__}:{obj.__class__.__name__})"
return str(obj)
def create_patch_proxy(target: Callable, new: Callable):
"""
Creates a proxy that calls `new` but passes as first argument the target.
"""
@functools.wraps(target)
def proxy(*args, **kwargs):
if _is_bound_method:
# bound object "self" is passed as first argument if this is a bound method
args = args[1:]
return new(target, *args, **kwargs)
# keep track of the real proxy subject (i.e., the new function that is used as patch)
proxy.__subject__ = new
_is_bound_method = inspect.ismethod(target)
if _is_bound_method:
proxy = types.MethodType(proxy, target.__self__)
return proxy
class Patch:
applied_patches: list["Patch"] = []
"""Bookkeeping for patches that are applied. You can use this to debug patches. For instance,
you could write something like::
for patch in Patch.applied_patches:
print(patch)
Which will output in a human readable format information about the currently active patches.
"""
obj: Any
name: str
new: Any
def __init__(self, obj: Any, name: str, new: Any) -> None:
super().__init__()
self.obj = obj
self.name = name
try:
self.old = getattr(self.obj, name)
except AttributeError:
self.old = None
self.new = new
self.is_applied = False
def apply(self):
if self.is_applied:
return
if self.old and self.name == "__getattr__":
raise Exception("You can't patch class types implementing __getattr__")
if not self.old and self.name != "__getattr__":
raise AttributeError(f"`{self.obj.__name__}` object has no attribute `{self.name}`")
setattr(self.obj, self.name, self.new)
Patch.applied_patches.append(self)
self.is_applied = True
def undo(self):
if not self.is_applied:
return
# If we added a method to a class type, we don't have a self.old. We just delete __getattr__
setattr(self.obj, self.name, self.old) if self.old else delattr(self.obj, self.name)
Patch.applied_patches.remove(self)
self.is_applied = False
def __enter__(self):
self.apply()
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.undo()
return self
@staticmethod
def extend_class(target: type, fn: Callable):
def _getattr(obj, name):
if name != fn.__name__:
raise AttributeError(f"`{target.__name__}` object has no attribute `{name}`")
return functools.partial(fn, obj)
return Patch(target, "__getattr__", _getattr)
@staticmethod
def function(target: Callable, fn: Callable, pass_target: bool = True):
obj = get_defining_object(target)
name = target.__name__
is_class_instance = not inspect.isclass(obj) and not inspect.ismodule(obj)
if is_class_instance:
# special case: If the defining object is not a class, but a class instance,
# then we need to bind the patch function to the target object. Also, we need
# to ensure that the final patched method has the same name as the original
# method on the defining object (required for restoring objects with patched
# methods from persistence, to avoid AttributeError).
fn.__name__ = name
fn = types.MethodType(fn, obj)
if pass_target:
new = create_patch_proxy(target, fn)
else:
new = fn
return Patch(obj, name, new)
def __str__(self):
try:
# try to unwrap the original underlying function that is used as patch (basically undoes what
# ``create_patch_proxy`` does)
new = self.new.__subject__
except AttributeError:
new = self.new
old = self.old
return f"Patch({to_metadata_string(old)} -> {to_metadata_string(new)}, applied={self.is_applied})"
class Patches:
patches: list[Patch]
def __init__(self, patches: list[Patch] = None) -> None:
super().__init__()
self.patches = []
if patches:
self.patches.extend(patches)
def apply(self):
for p in self.patches:
p.apply()
def undo(self):
for p in self.patches:
p.undo()
def __enter__(self):
self.apply()
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.undo()
def add(self, patch: Patch):
self.patches.append(patch)
def function(self, target: Callable, fn: Callable, pass_target: bool = True):
self.add(Patch.function(target, fn, pass_target))
def patch(target, pass_target=True):
"""
Function decorator to create a patch via Patch.function and immediately apply it.
Example::
def echo(string):
return "echo " + string
@patch(target=echo)
def echo_uppercase(target, string):
return target(string).upper()
echo("foo")
# will print "ECHO FOO"
echo_uppercase.patch.undo()
echo("foo")
# will print "echo foo"
When you are patching classes, with ``pass_target=True``, the unbound function will be passed as the first
argument before ``self``.
For example::
@patch(target=MyEchoer.do_echo, pass_target=True)
def my_patch(fn, self, *args):
return fn(self, *args)
@patch(target=MyEchoer.do_echo, pass_target=False)
def my_patch(self, *args):
...
This decorator can also patch a class type with a new method.
For example:
@patch(target=MyEchoer)
def new_echo(self, *args):
...
:param target: the function or method to patch
:param pass_target: whether to pass the target to the patching function as first parameter
:returns: the same function, but with a patch created
"""
@functools.wraps(target)
def wrapper(fn):
fn.patch = (
Patch.extend_class(target, fn)
if inspect.isclass(target)
else Patch.function(target, fn, pass_target=pass_target)
)
fn.patch.apply()
return fn
return wrapper