Question

给定一个函数对象，我该如何获得它的签名？例如，对于：

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

我想获得"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',))

但请注意，自Python 3.0以来，inspect.getargspec()已被弃用。

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

Python 3.5+推荐inspect.signature()。

Answer 2

可以说，找到函数签名的最简单方法是help(function)：

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

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

此外，在Python 3中，一个方法被添加到名为inspect的{{1}}模块中，该模块旨在表示signature of a callable object and its return annotation：

signature

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

尝试在对象上调用help以了解相关信息。

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

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

Answer 5

参加派对可能有点晚了，但如果您还想保留参数及其默认值的顺序，那么您可以使用Abstract Syntax Tree module (ast)。

这是一个概念证明（注意对参数进行排序并将它们与默认值匹配的代码肯定可以改进/更清楚）：

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

如果您要做的就是打印该功能，请使用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)

如果您正在尝试实际分析函数签名，请使用检查模块的argspec。在将用户的钩子脚本函数验证到一般框架中时，我必须这样做。

Answer 7

在命令行（IPython）中使用％pdef，它将仅打印签名。

例如%pdef np.loadtxt

 np.loadtxt(fname, dtype=<class 'float'>, comments='#', delimiter=None, converters=None, skiprows=0, usecols=None, unpack=False, ndmin=0, encoding='bytes')

Answer 8

示例代码：

import inspect
from collections import OrderedDict


def get_signature(fn):
    params = inspect.signature(fn).parameters
    args = []
    kwargs = OrderedDict()
    for p in params.values():
        if p.default is p.empty:
            args.append(p.name)
        else:
            kwargs[p.name] = p.default
    return args, kwargs


def test_sig():
    def fn(a, b, c, d=3, e="abc"):
        pass

    assert get_signature(fn) == (
        ["a", "b", "c"], OrderedDict([("d", 3), ("e", "abc")])
    )

如何读取函数的签名，包括默认参数值？

8 个答案: