我如何找到Python函数的参数个数？ [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正常参数以及多少个命名参数。

示例：

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

这个方法有2个参数和1个命名参数。

以前接受的答案是 弃用 Python 3.0 。现在，您应该选择替代它的 Signature 类，而不是使用 inspect.getargspec 。

通过 签名功能：

 从检查导入签名
 
 def someMethod（self，arg1，kwarg1 = None）：
 pass 
 $ b $ sig =签名（someMethod）
  

现在，您可以快速查看其参数 str ：

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

或者您还可以通过 sig.parameters 。



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

另外，您可以在<$ c上调用 len $ c> sig.parameters 也可以看到这个函数需要的参数个数：

  print（ len（params））＃3 
  

params mapping实际上是一个 参数 code>对象，它有更多的属性让你的生活更轻松。例如，抓取一个参数并查看它的默认值现在很容易执行：



  kwarg1 = params ['kwarg1'] 
 kwarg1.default＃返回：无
  

类似地，包含在参数。

---

至于Python 2。 x 用户，而 inspect.getargspec 不被使用，该语言很快就会变成:-)。 Signature 类在 2.x 系列中不可用，不会有。因此，您仍然需要使用 inspect.getargspec 。

至于Python 2和Python 3之间的转换，如果您的代码依赖于 Python 2中的getargspec 并且在 3 中切换到签名太困难了，您确实有宝贵的选择使用 inspect.getfullargspec 。它提供了一个与 getargspec （一个可调用参数）相似的接口，以便获取函数的参数，同时还处理 getargspec 不会：

  from inspect import getfullargspec 
 
 def someMethod（self ，arg1，kwarg1 = None）：
 pass 
 
 args = getfullargspec（someMethod）
  

与 getargspec 一样， getfullargspec 返回一个 NamedTuple


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

Example:
def someMethod(self, arg1, kwarg1=None):
    pass
This method has 2 arguments and 1 named argument.
解决方案
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 Instead of using inspect.getargspec you should now opt for the Signature class which superseded it. 

Creating a Signature for the function is easy via the signature function:
from inspect import signature

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

sig = signature(someMethod)
Now, you can either view its parameters quickly by string it:
str(sig)  # returns: '(self, arg1, kwarg1=None)'
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
Additionally, you can call len on sig.parameters to also see the number of arguments this function requires:
print(len(params))  # 3
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
similarly for the rest of the objects contained in parameters.



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.

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)
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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