如何讀取包含默認參數值的函數簽名？

Question

給定一個函數對象，我怎樣才能得到它的簽名？例如，用於：

def myMethod(firt, second, third='something'): 
    pass 

我想獲得"myMethod(firt, second, third='something')"。

Answer 1

import inspect 

def foo(a, b, x='blah'): 
    pass 

print(inspect.getargspec(foo)) 
# ArgSpec(args=['a', 'b', 'x'], varargs=None, keywords=None, defaults=('blah',)) 

但是，請注意因爲Python 3.0 inspect.getargspec()已被棄用。

Python 3.0--3.4推薦inspect.getfullargspec()。

Python 3.5+推薦inspect.signature()。

Answer 2

嘗試在對象上調用help以瞭解它。

>>> foo = [1, 2, 3] 
>>> help(foo.append) 
Help on built-in function append: 

append(...) 
    L.append(object) -- append object to end 

Answer 3

#! /usr/bin/env python 

import inspect 
from collections import namedtuple 

DefaultArgSpec = namedtuple('DefaultArgSpec', 'has_default default_value') 

def _get_default_arg(args, defaults, arg_index): 
    """ Method that determines if an argument has default value or not, 
    and if yes what is the default value for the argument 

    :param args: array of arguments, eg: ['first_arg', 'second_arg', 'third_arg'] 
    :param defaults: array of default values, eg: (42, 'something') 
    :param arg_index: index of the argument in the argument array for which, 
    this function checks if a default value exists or not. And if default value 
    exists it would return the default value. Example argument: 1 
    :return: Tuple of whether there is a default or not, and if yes the default 
    value, eg: for index 2 i.e. for "second_arg" this function returns (True, 42) 
    """ 
    if not defaults: 
     return DefaultArgSpec(False, None) 

    args_with_no_defaults = len(args) - len(defaults) 

    if arg_index < args_with_no_defaults: 
     return DefaultArgSpec(False, None) 
    else: 
     value = defaults[arg_index - args_with_no_defaults] 
     if (type(value) is str): 
      value = '"%s"' % value 
     return DefaultArgSpec(True, value) 

def get_method_sig(method): 
    """ Given a function, it returns a string that pretty much looks how the 
    function signature would be written in python. 

    :param method: a python method 
    :return: A string similar describing the pythong method signature. 
    eg: "my_method(first_argArg, second_arg=42, third_arg='something')" 
    """ 

    # The return value of ArgSpec is a bit weird, as the list of arguments and 
    # list of defaults are returned in separate array. 
    # eg: ArgSpec(args=['first_arg', 'second_arg', 'third_arg'], 
    # varargs=None, keywords=None, defaults=(42, 'something')) 
    argspec = inspect.getargspec(method) 
    arg_index=0 
    args = [] 

    # Use the args and defaults array returned by argspec and find out 
    # which arguments has default 
    for arg in argspec.args: 
     default_arg = _get_default_arg(argspec.args, argspec.defaults, arg_index) 
     if default_arg.has_default: 
      args.append("%s=%s" % (arg, default_arg.default_value)) 
     else: 
      args.append(arg) 
     arg_index += 1 
    return "%s(%s)" % (method.__name__, ", ".join(args)) 


if __name__ == '__main__': 
    def my_method(first_arg, second_arg=42, third_arg='something'): 
     pass 

    print get_method_sig(my_method) 
    # my_method(first_argArg, second_arg=42, third_arg="something") 

Answer 4

按理說找到某個函數的簽名將help(function)最簡單的方法：

>>> def function(arg1, arg2="foo", *args, **kwargs): pass 
>>> help(function) 
Help on function function in module __main__: 

function(arg1, arg2='foo', *args, **kwargs) 

另外，在Python 3加入到inspect模塊稱爲signature，其被設計來表示的方法在signature of a callable object and its return annotation：

>>> from inspect import signature 
>>> def foo(a, *, b:int, **kwargs): 
...  pass 

>>> sig = signature(foo) 

>>> str(sig) 
'(a, *, b:int, **kwargs)' 

>>> str(sig.parameters['b']) 
'b:int' 

>>> sig.parameters['b'].annotation 
<class 'int'> 

Answer 5

也許有點遲到了，但如果你也想保持一個順序參數和它們的默認值，那麼你可以使用Abstract Syntax Tree module (ast)。

這裏有一個概念證明（注意代碼的參數進行排序，並將其匹配爲默認值，絕對可以提高/變得更加清晰）：

import ast 

for class_ in [c for c in module.body if isinstance(c, ast.ClassDef)]: 
    for method in [m for m in class_.body if isinstance(m, ast.FunctionDef)]: 
     args = [] 
     if method.args.args: 
      [args.append([a.col_offset, a.id]) for a in method.args.args] 
     if method.args.defaults: 
      [args.append([a.col_offset, '=' + a.id]) for a in method.args.defaults] 
     sorted_args = sorted(args) 
     for i, p in enumerate(sorted_args): 
      if p[1].startswith('='): 
       sorted_args[i-1][1] += p[1] 
     sorted_args = [k[1] for k in sorted_args if not k[1].startswith('=')] 

     if method.args.vararg: 
      sorted_args.append('*' + method.args.vararg) 
     if method.args.kwarg: 
      sorted_args.append('**' + method.args.kwarg) 

     signature = '(' + ', '.join(sorted_args) + ')' 

     print method.name + signature 

Answer 6

如果你正在試圖做的一切都是打印該函數然後使用pydoc。

import pydoc  

def foo(arg1, arg2, *args, **kwargs):                  
    '''Some foo fn'''                      
    pass                         

>>> print pydoc.render_doc(foo).splitlines()[2] 
foo(arg1, arg2, *args, **kwargs) 

如果您嘗試實際分析函數簽名，則使用檢查模塊的argspec。在將用戶的鉤子腳本函數驗證爲通用框架時，我必須這樣做。