装饰器不传递参数？

Question

我一直致力于将 n 维数组序列化为一维“数组”数据库：

from collections import Iterable, Mapping
import sqlite3

def pass_many(vals, some_funct, args=()):
    if not vals:
        return
    if isinstance(vals, Iterable) and not isinstance(vals, (basestring, Mapping)):
        for v in vals:
            pass_many(v, some_funct, args)
    else:
        some_funct(vals, *args)

def counter(func):
    def wrapper(v, *args, **kwargs): # added 'v' arg to no avail
        wrapper.count = wrapper.count + 1
        test_var_args(v, *args, **kwargs)
        #return func(*args, **kwargs)
    wrapper.count = 0

    return wrapper

def test_var_args(farg, *args):
    print "formal arg:", farg
    for arg in args:
        print "another arg:", arg

@counter
def insert(val, cursor, table="wordlist", logfile="queries.log"):
    print val, cursor, table, logfile
    if val:
        if isinstance(val, (basestring, Mapping)):
            val = '\"' + val + '\"'
        else: val = str(val)
        query = "insert into tablename values (?);".replace('tablename', table).replace('?', val)
        #if logfile: to_logfile(query + '\n', logfile)
        cursor.execute(query)

if __name__ == '__main__':
    connection = sqlite3.connect('andthensome.db')
    cursor = connection.cursor()
    cursor.execute("create table array (word text);")
    pass_many([["foo", "bar"], "pew"], insert, cursor)
    connection.commit()
    cursor.execute("select * from array;") # wrapped select function omitted for brevity
    print "insert() was called", insert.count, "times, and db now contains:\n", cursor.fetchall()
    cursor.close()

输出：

formal arg: foo
formal arg: bar
formal arg: pew
insert() was called 3 times, and db now contains:
[]

输出取消注释#return func(*args, **kwargs):

formal arg: foo
Traceback (most recent call last):
    Line 42, in <module>
        pass_many([["foo", "bar"], "pew"], insert, cursor)
    Line 9, in pass_many
        pass_many(v, some_funct, args)
    Line 9, in pass_many
        pass_many(v, some_funct, args)
    Line 11, in pass_many
        some_funct(vals, *args)
    Line 17, in wrapper
        return func(*args, **kwargs)
    TypeError: insert() takes at least 2 arguments (0 given)

预期输出（省略调试功能）：

insert() was called 3 times, and db now contains:
["foo","bar","pew"]

不幸的是，用counter 装饰的insert 函数似乎没有正确传递参数。

我做错了什么？

Answer 1

一个问题似乎是您正在使用*args 来扩展您的args 参数，但是您将cursor 作为该参数的值传入而没有将其包装在一个元组中。因此，当您似乎希望它是 insert("foo", cursor) 时，您的最终呼叫是 insert("foo", *cursor)。试试pass_many([["foo", "bar"], "pew"], insert, (cursor,))。

我认为正在发生的事情是，当您这样做时，您的 test_var_args 函数正在消耗光标对象（这显然是可迭代的），因此在随后调用真正的 insert 时不再留下更多参数来扩展功能。

在您回复后编辑：您真的不想将v 传递给您的func 电话吗？你写的插入函数有两个参数，v 和cursor，但你只用cursor 调用它。你为什么要包装insert？额外的参数应该做什么？你没有在包装器中使用它，也没有将它传递给底层函数，那么它的目的是什么？

Answer 2

根据@BrenBarn 的建议，我已将其修改为：

def counter(func):
    def wrapper(v, *args, **kwargs):
        wrapper.count = wrapper.count + 1
        test_var_args(v, *args, **kwargs)
        return func(v, *args, **kwargs)
    wrapper.count = 0

    return wrapper

pass_many([["foo", "bar"], "pew"], insert, [cursor])

Answer 3

有几件事：首先，在wrapper()：

def counter(func):
    def wrapper(v, *args, **kwargs): # added 'v' arg to no avail
        wrapper.count = wrapper.count + 1
        test_var_args(v, *args, **kwargs)
        return func(*args, **kwargs)
    ...

您已将第一个参数映射到v，但您没有将它传递给真正的func。最好彻底删除。

其次，也是最重要的：

def pass_many(vals, some_funct, args=()):
    if not vals:
        return
    if isinstance(vals, Iterable) and not isinstance(vals, (basestring, Mapping)):
        for v in vals:
            pass_many(v, some_funct, args)
    else:
        some_funct(vals, *args)

请注意，当您调用some_funct() 时，您正在解构args 参数。问题是，当你调用pass_many() 时，你给了它一个cursor 对象作为args 参数。这将巧妙地失败。要解决此问题，您可以删除 splat 运算符 *，或者，更好的选择是，您可以在调用 pass_many 时将 cursor 对象包装在一个元组中，如下所示：

pass_many([["foo", "bar"], "pew"], insert, (cursor,))

这仍然会报“no such table: wordlist”的错误，但这实际上是因为你没有定义这样的表。 （'wordlist' 是 insert() 的默认参数）