简述python中`functools.wrapper()

简述python中functools.wrapper()

首先对于最简单的函数：

def a(): pass if __name__ == '__main__': print(a.__name__)

输出结果：

a

然后稍微复杂点：

def a(func): def wrapper() return func @a def b(): pass if __name__ == '__main__' print(b.__name__)

输出结果：

a

当加上functools.wrapper时：

def a(func): @functools.wrapper(func) def wrapper() return func @a def b(): pass if __name__ == '__main__' print(b.__name__)

输出结果：

b

很明显，通过调用functools.wrapper()使得返回值发生了改变，这其实与它的函数定义有关，代码如下：

def wraps(wrapped, assigned = WRAPPER_ASSIGNMENTS, updated = WRAPPER_UPDATES): """Decorator factory to apply update_wrapper() to a wrapper function Returns a decorator that invokes update_wrapper() with the decorated function as the wrapper argument and the arguments to wraps() as the remaining arguments. Default arguments are as for update_wrapper(). This is a convenience function to simplify applying partial() to update_wrapper(). """ return partial(update_wrapper, wrapped=wrapped, assigned=assigned, updated=updated) def update_wrapper(wrapper, wrapped, assigned = WRAPPER_ASSIGNMENTS, updated = WRAPPER_UPDATES): """Update a wrapper function to look like the wrapped function wrapper is the function to be updated wrapped is the original function assigned is a tuple naming the attributes assigned directly from the wrapped function to the wrapper function (defaults to functools.WRAPPER_ASSIGNMENTS) updated is a tuple naming the attributes of the wrapper that are updated with the corresponding attribute from the wrapped function (defaults to functools.WRAPPER_UPDATES) """ for attr in assigned: try: value = getattr(wrapped, attr) except AttributeError: pass else: setattr(wrapper, attr, value) for attr in updated: getattr(wrapper, attr).update(getattr(wrapped, attr, {})) # Issue #17482: set __wrapped__ last so we don't inadvertently copy it # from the wrapped function when updating __dict__ wrapper.__wrapped__ = wrapped # Return the wrapper so this can be used as a decorator via partial() return wrapper class partial: """New function with partial application of the given arguments and keywords. """ __slots__ = "func", "args", "keywords", "__dict__", "__weakref__" def __new__(cls, func, /, *args, **keywords): if not callable(func): raise TypeError("the first argument must be callable") if hasattr(func, "func"): args = func.args + args keywords = {**func.keywords, **keywords} func = func.func self = super(partial, cls).__new__(cls) self.func = func self.args = args self.keywords = keywords return self def __call__(self, /, *args, **keywords): keywords = {**self.keywords, **keywords} return self.func(*self.args, *args, **keywords) @recursive_repr() def __repr__(self): qualname = type(self).__qualname__ args = [repr(self.func)] args.extend(repr(x) for x in self.args) args.extend(f"{k}={v!r}" for (k, v) in self.keywords.items()) if type(self).__module__ == "functools": return f"functools.{qualname}({', '.join(args)})" return f"{qualname}({', '.join(args)})" def __reduce__(self): return type(self), (self.func,), (self.func, self.args, self.keywords or None, self.__dict__ or None) def __setstate__(self, state): if not isinstance(state, tuple): raise TypeError("argument to __setstate__ must be a tuple") if len(state) != 4: raise TypeError(f"expected 4 items in state, got {len(state)}") func, args, kwds, namespace = state if (not callable(func) or not isinstance(args, tuple) or (kwds is not None and not isinstance(kwds, dict)) or (namespace is not None and not isinstance(namespace, dict))): raise TypeError("invalid partial state") args = tuple(args) # just in case it's a subclass if kwds is None: kwds = {} elif type(kwds) is not dict: # XXX does it need to be *exactly* dict? kwds = dict(kwds) if namespace is None: namespace = {} self.__dict__ = namespace self.func = func self.args = args self.keywords = kwds try: from _functools import partial except ImportError: pass

上面大致讲的呢，就是通过调用functools.wrappers()来创建了不一样的函数，但是名字却是一样的，且id不一样，功能也可能会有所改变。代码如下：

import functools def m(func): print(func.__name__) print(id(func)) @functools.wraps(func) def wrapper(): print(wrapper.__name__) print(id(wrapper)) return wrapper def method1(): pass @m def method2(): print(id(method2)) if __name__ == '__main__': print(method2())

输出：

method2 1868266070224 method2 1868266070368 None

综上：调用该函数创建了另一个名字一样的函数，但是内部构造可能会不相同。