如何将非硬编码参数传递给 Python 装饰器？

Question

我的目标是创建一个简单的单元测试装饰器，它执行一个函数，如果成功，则什么也不做，如果不成功，则打印“FAILURE”及其所有参数。我确实知道内置的 unittest 包。我这样做是为了学习装饰器。我没有比“如果实际等于预期，什么也不做，否则打印参数”更进一步。

我找到了this function，它打印出一个函数的所有参数：

def dumpArgs(func):
    '''Decorator to print function call details - parameters names and effective values'''
    def wrapper(*func_args, **func_kwargs):
        arg_names = func.__code__.co_varnames[:func.__code__.co_argcount]
        args = func_args[:len(arg_names)]
        defaults = func.__defaults__ or ()
        args = args + defaults[len(defaults) - (func.__code__.co_argcount - len(args)):]
        params = list(zip(arg_names, args))
        args = func_args[len(arg_names):]
        if args: params.append(('args', args))
        if func_kwargs: params.append(('kwargs', func_kwargs))
        print(func.__name__ + ' (' + ', '.join('%s = %r' % p for p in params) + ' )')
        return func(*func_args, **func_kwargs)
    return wrapper

@dumpArgs
def test(a, b = 4, c = 'blah-blah', *args, **kwargs):
    pass

test(1)
test(1, 3)
test(1, d = 5)
test(1, 2, 3, 4, 5, d = 6, g = 12.9)

输出：

test (a = 1, b = 4, c = 'blah-blah' )
test (a = 1, b = 3, c = 'blah-blah' )
test (a = 1, b = 4, c = 'blah-blah', kwargs = {'d': 5} )
test (a = 1, b = 2, c = 3, args = (4, 5), kwargs = {'g': 12.9, 'd': 6} )

我把它改成了这个，只有当函数不等于4时才打印出参数（在没有装饰器参数的情况下实现）：

def get_all_func_param_name_values(func, *func_args, **func_kwargs):
    arg_names = func.__code__.co_varnames[:func.__code__.co_argcount]
    args = func_args[:len(arg_names)]
    defaults = func.__defaults__ or ()
    args = args + defaults[len(defaults) - (func.__code__.co_argcount - len(args)):]
    params = list(zip(arg_names, args))
    args = func_args[len(arg_names):]
    if args: params.append(('args', args))
    if func_kwargs: params.append(('kwargs', func_kwargs))
    return  '(' + ', '.join('%s = %r' % p for p in params) + ')'

def dumpArgs(func):
    '''Decorator to print function call details - parameters names and effective values'''
    def wrapper(*func_args, **func_kwargs):
        a = func(*func_args, **func_kwargs)
        if(a != 4):
            return  a
        print("FAILURE: " + func.__name__ + get_all_func_param_name_values(func, *func_args, **func_kwargs))
        return a
    return wrapper

@dumpArgs
def getA(a, b = 4, c = 'blah-blah', *args, **kwargs):
    return  a

getA(1)
getA(1, 3)
getA(4, d = 5)
getA(1, 2, 3, 4, 5, d = 6, g = 12.9)

输出：

FAILURE: getA(a = 4, b = 4, c = 'blah-blah', kwargs = {'d': 5})
Out[21]: 1

（我不明白为什么1 会打印在第二行。）

然后我将其更改为传入预期值4，作为装饰器参数。如this answer 中所述，它要求原始装饰器是嵌套函数：

def get_all_func_param_name_values(func, *func_args, **func_kwargs):
    arg_names = func.__code__.co_varnames[:func.__code__.co_argcount]
    args = func_args[:len(arg_names)]
    defaults = func.__defaults__ or ()
    args = args + defaults[len(defaults) - (func.__code__.co_argcount - len(args)):]
    params = list(zip(arg_names, args))
    args = func_args[len(arg_names):]
    if args: params.append(('args', args))
    if func_kwargs: params.append(('kwargs', func_kwargs))
    return  '(' + ', '.join('%s = %r' % p for p in params) + ')'

def dumpArgs(expected_value):
    def dumpArgs2(func):
        '''Decorator to print function call details - parameters names and effective values'''
        def wrapper(*func_args, **func_kwargs):
            a = func(*func_args, **func_kwargs)
            if(a == expected_value):
                return  a
            print("FAILURE: " + func.__name__ + get_all_func_param_name_values(func, *func_args, **func_kwargs))
            return a
        return wrapper
    return  dumpArgs2

@dumpArgs(4)
def getA(a, b = 4, c = 'blah-blah', *args, **kwargs):
    return  a

getA(1)
getA(1, 3)
getA(4, d = 5)
getA(1, 2, 3, 4, 5, d = 6, g = 12.9)

输出：

FAILURE: getA(a = 1, b = 4, c = 'blah-blah')
FAILURE: getA(a = 1, b = 3, c = 'blah-blah')
FAILURE: getA(a = 1, b = 2, c = 3, args = (4, 5), kwargs = {'g': 12.9, 'd': 6})
Out[31]: 1

（同样，1...）

我不清楚如何将这个硬编码的4 更改为expected_value 参数，该参数在每个函数调用中都会传递。我见过的所有示例（如this one）都有硬编码参数。

我目前正在尝试

assert_expected_func_params(4, getA, 1)
assert_expected_func_params(4, getA, 1, 3)
assert_expected_func_params(4, getA, 4, d = 5)
assert_expected_func_params(4, getA, 1, 2, 3, 4, 5, d = 6, g = 12.9)

但它远没有工作。

如何实现可以传递给每个函数调用的装饰器参数？

Answer 1

由于装饰器包装了函数，因此可以在调用时截取函数的输入和输出。这样，您可以查找 _expected 关键字，将其剥离，调用函数，然后根据传入的预期值测试函数的返回值。

from functools import wraps

_empty = object()  # sentinel value used to control testing

def dump_ne(func):
    @wraps(func)
    def decorated(*args, **kwargs):
        # remove the expected value from the actual call kwargs
        expected = kwargs.pop('_expected', _empty)

        # call the function with rest of args and kwargs
        result = func(*args, **kwargs)

        # only test when _expected was passed in the kwargs
        # only print when the result didn't equal expected
        if expected is not _empty and expected != result:
            print('FAIL: func={}, args={}, kwargs={}'.format(func.__name__, args, kwargs))

        return result

    return decorated

@dump_ne
def cool(thing):
    return thing.upper()

print(cool('cat'))  # prints 'CAT', test isn't run

for thing in ('cat', 'ice', 'cucumber'):
    print(cool(thing, _expected='CUCUMBER'))
    # dumps info for first 2 calls (cat, ice)