迭代Python中的dict或列表

Question

刚写了一些讨厌的代码,它们迭代在Python dict或者listPython中.我觉得这不是最好的方法.

问题是,为了迭代dict,这是惯例:

for key in dict_object:
    dict_object[key] = 1

但是,如果在列表上执行相同的操作,则按键修改对象属性不起作用:

# Throws an error because the value of key is the property value, not 
#     the list index:

for key in list_object:
    list_object[key] = 1 

我解决这个问题的方法是编写这个讨厌的代码:

if isinstance(obj, dict):
    for key in obj:
        do_loop_contents(obj, key)
elif isinstance(obj, list):
    for i in xrange(0, len(obj)):
        do_loop_contents(obj, i)

def do_loop_contents(obj, key):
    obj[key] = 1

有一个更好的方法吗？

谢谢!

Answer 1

我永远不需要这样做.但如果我这样做,我可能会这样做:

seq_iter = x if isinstance(x, dict) else xrange(len(x))

例如,在函数形式中:

>>> def seq_iter(obj):
...     return obj if isinstance(obj, dict) else xrange(len(obj))
... 
>>> x = [1,2,3]
>>> for i in seq_iter(x):
...     x[i] = 99
... 
>>> x
[99, 99, 99]
>>> 
>>> x = {1: 2, 2:3, 3:4}
>>> for i in seq_iter(x):
...     x[i] = 99
... 
>>> x
{1: 99, 2: 99, 3: 99}

Answer 2

这是正确的方法,但如果由于某种原因你需要以相同的方式处理这两个对象,你可以创建一个可以返回索引/键的迭代,无论如何:

def common_iterable(obj):
    if isinstance(obj, dict):
        return obj
    else:
        return (index for index, value in enumerate(obj))

哪个会以您想要的方式表现:

>>> d = {'a': 10, 'b': 20}
>>> l = [1,2,3,4]
>>> for index in common_iterable(d):
    d[index] = 0

>>> d
{'a': 0, 'b': 0}
>>> for index in common_iterable(l):
    l[index] = 0

>>> l
[0, 0, 0, 0]

或者可能更有效率,使用发电机:

def common_iterable(obj):
    if isinstance(obj, dict):
        for key in obj:
            yield key
    else:
        for index, value in enumerate(obj):
            yield index

Answer 3

要成为 pythonic 和ducktype-y，并遵循“请求宽恕而不是许可”，您可以执行以下操作：

try:
    iterator = obj.iteritems()
except AttributeError:
    iterator = enumerate(obj)
for reference, value in iterator:
    do_loop_contents(obj, reference)

虽然如果您只需要键/索引：

try:
    references = obj.keys()
except AttributeError:
    references = range(len(obj))
for reference in references:
    do_loop_contents(obj, reference)

或者作为一个函数：

def reference_and_value_iterator(iterable):
    try:
        return iterable.iteritems()
    except AttributeError:
        return enumerate(iterable)

for reference, value in reference_and_value_iterator(obj):
    do_loop_contents(obj, reference)

或者只是参考：

def references(iterable):
    try:
        return iterable.keys()
    except AttributeError:
        return range(len(iterable))

for reference in references(obj):
    do_loop_contents(obj, reference)