1-Python - 关于functools模块的wraps装饰器用途
测试环境：Python3.6.2 + win10 + Pycharm2017.3
装饰器之functools模块的wraps的用途：
首先我们先写一个装饰器
# 探索functools模块wraps装饰器的用途 from functools import wraps def trace(func): """ 装饰器 """ # @wraps(func) def callf(*args, **kwargs): """ A wrapper function """ print("Calling function:{}".format(func.__name__)) # Calling function:foo res = func(*args, **kwargs) print("Return value:{}".format(res)) # Return value:9 return res return callf @trace def foo(x): """ 返回给定数字的平方 """ return x * x if __name__ == '__main__': print(foo(3)) # 9 print(foo.__doc__) help(foo) print(foo.__name__) # print(foo.__globals__) t = trace(foo) print(t) 打印结果： Calling function:foo Return value:9 9 A wrapper function Help on function callf in module __main__: callf(*args, **kwargs) A wrapper function callf <function trace.<locals>.callf at 0x0000022F744D8730>
上面的装饰器例子等价于：trace(foo(3)),只是在使用装饰器时，我们不用再手动调用装饰器函数；
如果把这段代码提供给其他人调用， 他可能会想看下foo函数的帮助信息时：
>>>from xxx import foo
>>>help(foo) # print(foo__doc__)
Help on function callf in module __main__:
callf(*args, **kwargs)
A wrapper function
这里，他可能会感到迷惑，继续敲：
>>> print(foo.__name__) callf
最后， 他可能会看源码，找问题原因，我们知道Python中的对象都是"第一类"的，所以，trace函数会返回一个callf闭包函数，连带callf的上下文环境一并返回，所以，可以解释我们执行help(foo)的到结果了
那么，我们如果才能得到我们想要的foo的帮助信息呢，这里就要用到了functools的wraps了。
# 探索functools模块wraps装饰器的用途 from functools import wraps def trace(func): """ 装饰器 """ @wraps(func) def callf(*args, **kwargs): """ A wrapper function """ print("Calling function:{}".format(func.__name__)) # Calling function:foo res = func(*args, **kwargs) print("Return value:{}".format(res)) # Return value:9 return res return callf @trace def foo(x): """ 返回给定数字的平方 """ return x * x if __name__ == '__main__': print(foo(3)) # 9 print(foo.__doc__) help(foo) print(foo.__name__) # print(foo.__globals__) t = trace(foo) print(t)
至于wraps的原理，通过下面部分源码，可以自行研究，在此就不予展开扩展了
# 有关wraps的源码，有兴趣的可以自行研究下 WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__qualname__', '__doc__', '__annotations__') WRAPPER_UPDATES = ('__dict__',) 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 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) class partial: """New function with partial application of the given arguments and keywords. """ __slots__ = "func", "args", "keywords", "__dict__", "__weakref__" def __new__(*args, **keywords): if not args: raise TypeError("descriptor '__new__' of partial needs an argument") if len(args) < 2: raise TypeError("type 'partial' takes at least one argument") cls, func, *args = args if not callable(func): raise TypeError("the first argument must be callable") args = tuple(args) if hasattr(func, "func"): args = func.args + args tmpkw = func.keywords.copy() tmpkw.update(keywords) keywords = tmpkw del tmpkw func = func.func self = super(partial, cls).__new__(cls) self.func = func self.args = args self.keywords = keywords return self def __call__(*args, **keywords): if not args: raise TypeError("descriptor '__call__' of partial needs an argument") self, *args = args newkeywords = self.keywords.copy() newkeywords.update(keywords) return self.func(*self.args, *args, **newkeywords) @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
只要是知道，wraps是通过partial和update_wrapper来帮我们实现想要的结果的
摘自：
https://www.cnblogs.com/myd7349/p/how_to_use_wraps_of_functools.html # 关于functools模块的wraps装饰器
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