How can I read a function's signature including default argument values?
给定一个函数对象,我该如何获得它的签名? 例如,对于:
1 2 | def myMethod(firt, second, third='something'): pass |
我想得到
1 2 3 4 5 6 7 | 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,不推荐使用
Python 3.0--3.4推荐
Python 3.5+建议使用
可以说,找到函数签名的最简单方法是
1 2 3 4 5 | >>> 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,一个名为
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | >>> 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'> |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 | #! /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") |
尝试在对象上调用
1 2 3 4 5 6 | >>> foo = [1, 2, 3] >>> help(foo.append) Help on built-in function append: append(...) L.append(object) -- append object to end |
也许派对有点晚了,但是如果你还想保持参数的顺序和它们的默认值,那么你可以使用抽象语法树模块(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/更清晰):
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | 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 |
如果你要做的只是打印函数,那么使用pydoc。
1 2 3 4 5 6 7 8 | 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。
示例代码:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | 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")]) ) |
在命令行(IPython)中使用%pdef,它将仅打印签名。
例如
1 | np.loadtxt(fname, dtype=<class 'float'>, comments='#', delimiter=None, converters=None, skiprows=0, usecols=None, unpack=False, ndmin=0, encoding='bytes') |