如何找到 Python 函数的参数数量? [英] How can I find the number of arguments of a Python function?

问题描述

如何找到 Python 函数的参数数量?我需要知道它有多少个普通参数和多少个命名参数.

How can I find the number of arguments of a Python function? I need to know how many normal arguments it has and how many named arguments.

示例:

def someMethod(self, arg1, kwarg1=None):
    pass

此方法有 2 个参数和 1 个命名参数.

This method has 2 arguments and 1 named argument.

推荐答案

之前接受的答案是 不推荐使用，从 Python 3.0 开始.您现在应该选择取代它的 Signature 类，而不是使用 inspect.getargspec.

The previously accepted answer has been deprecated as of Python 3.0. Instead of using inspect.getargspec you should now opt for the Signature class which superseded it.

通过签名很容易为函数创建签名 函数:

from inspect import signature

def someMethod(self, arg1, kwarg1=None):
    pass

sig = signature(someMethod)

现在，您可以通过 str 快速查看其参数:

Now, you can either view its parameters quickly by string it:

str(sig)  # returns: '(self, arg1, kwarg1=None)'

或者您也可以通过 sig.parameters 获得属性名称到参数对象的映射.

or you can also get a mapping of attribute names to parameter objects via sig.parameters.

params = sig.parameters 
print(params['kwarg1']) # prints: kwarg1=20

此外，您可以在 sig.parameters 上调用 len 来查看此函数需要的参数数量:

Additionally, you can call len on sig.parameters to also see the number of arguments this function requires:

print(len(params))  # 3

params 映射中的每个条目实际上都是一个 Parameter 对象 具有更多属性，使您的生活更轻松.例如，现在可以轻松地获取参数并查看其默认值:

Each entry in the params mapping is actually a Parameter object that has further attributes making your life easier. For example, grabbing a parameter and viewing its default value is now easily performed with:

kwarg1 = params['kwarg1']
kwarg1.default # returns: None

对于参数中包含的其余对象也是如此.

similarly for the rest of the objects contained in parameters.

对于 Python 2.x 用户来说，虽然 inspect.getargspec 没有 被弃用，但该语言很快就会:-).Signature 类在 2.x 系列中不可用，也不会.所以你仍然需要使用 inspect.getargspec.

As for Python 2.x users, while inspect.getargspec isn't deprecated, the language will soon be :-). The Signature class isn't available in the 2.x series and won't be. So you still need to work with inspect.getargspec.

至于在 Python 2 和 3 之间的转换，如果您的代码依赖于 Python 2 中的 getargspec 接口并切换到 3signature/code> 太难了，你确实有使用 ="noreferrer">inspect.getfullargspec.它提供了与 getargspec(单个可调用参数)类似的接口，以便获取函数的参数，同时还处理一些 getargspec 没有的其他情况:

As for transitioning between Python 2 and 3, if you have code that relies on the interface of getargspec in Python 2 and switching to signature in 3 is too difficult, you do have the valuable option of using inspect.getfullargspec. It offers a similar interface to getargspec (a single callable argument) in order to grab the arguments of a function while also handling some additional cases that getargspec doesn't:

from inspect import getfullargspec

def someMethod(self, arg1, kwarg1=None):
    pass

args = getfullargspec(someMethod)

与 getargspec 一样，getfullargspec 返回一个包含参数的 NamedTuple.

As with getargspec, getfullargspec returns a NamedTuple which contains the arguments.

print(args)
FullArgSpec(args=['self', 'arg1', 'kwarg1'], varargs=None, varkw=None, defaults=(None,), kwonlyargs=[], kwonlydefaults=None, annotations={})

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