[英]counting the number of values in a specific key for a python dictionary
Can someone explain this to me, and/or direct me on the right/pythonic way of doing this? 有人可以向我解释一下,和/或指导我这样做的正确/ Python方式吗?
Python 2.7. Python 2.7。
Ultimately, I am trying to loop through dictionary countsD: 最终,我试图遍历字典countsD:
countsD = {"aa": None, "bb": None, "cc": None, "dd": None}
and for the match in a corresponding dictionary d: 对于相应字典d中的匹配项:
d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (45, 98), "dd": (1, 33)}
add the count of items as a value to the corresponding matching key, to create finally this countsD 将项目计数作为值添加到相应的匹配键中,以最终创建此countsD
{"aa": 6, "bb": 3, "cc": 2, "dd": 2}
If I do this with the above 如果我这样做以上
> d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (45, 98), "dd": (1, 33)}
> for key in d:
>> print(key)
>> print(len(d[key]))
Returned is this, which is what I want 返回的是这个,这就是我想要的
aa
6
cc
2
dd
2
bb
3
HOWEVER, if one of the values for a key only contains 1 value (entirely possible), like (see "cc"): 但是,如果某个键的值之一仅包含1个值(完全可能),例如(请参见“ cc”):
d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (45), "dd": (1, 33)}
and then run the same for loop, I get an error on the "cc" key: 然后运行相同的for循环,我在“ cc”键上收到错误消息:
aa
6
cc
Traceback (most recent call last):
File "<interactive input>", line 3, in <module>
TypeError: object of type 'int' has no len()
HOWEVER again, if I make that "cc" key have an empty value (), then all is fine again. 但是,如果我使“ cc”键具有空值(),那么一切都很好。
d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (), "dd": (1, 33)}
>>> d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (), "dd": (1, 33)}
>>> for key in d:
... print(key)
... print(len(d[key]))
...
aa
6
cc
0
dd
2
bb
3
And in typing the title for this post just now, I was referred to Count number of values in dictionary for each key for an answer. 在刚才输入此帖子的标题时,我被引用为字典中每个答案的键的计数值个数 。 Great, one line!
太好了,一行! But again, for a key with just one value, it fails.
但是同样,对于只有一个值的键,它会失败。 This good:
这个好:
>>> d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (), "dd": (1, 33)}
>>> new_countsD = {k: len(v) for k,v in d.items()}
>>> new_countsD
{'aa': 6, 'bb': 3, 'cc': 0, 'dd': 2}
this not, see key "cc" 这不是,请参见键“ cc”
>>> d = {"aa": (5689, 34, 44, 77, 88, 321), "bb": (33, 6742, 89744), "cc": (111), "dd": (1, 33)}
>>> new_countsD = {k: len(v) for k,v in d.items()}
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "<interactive input>", line 1, in <dictcomp>
TypeError: object of type 'int' has no len()
So, what gives?? 那么,什么给了? I feel like I am missing something stupid...
我觉得我想念一些愚蠢的东西...
Thanks for any help! 谢谢你的帮助!
In python, a single-item tuple (called a singleton) is written as (value,)
, so the (111)
in your input should be written as (111,)
instead; 在python中,单项元组(称为单例)写为
(value,)
,因此输入中的(111)
应该写为(111,)
; otherwise it would be considered an integer of 111
. 否则将被视为
111
的整数。
From tuple
's documentation : 从
tuple
的文档中 :
A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these.
一个特殊的问题是包含0或1项的元组的构造:语法具有一些额外的怪癖来容纳这些项。 Empty tuples are constructed by an empty pair of parentheses;
空元组由一对空括号组成; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses).
一个带有一个项目的元组是通过在值后面加上逗号来构造的(仅将一个值括在括号中是不够的)。 Ugly, but effective.
难看,但是有效。
>>> empty = () >>> singleton = 'hello', # <-- note trailing comma >>> len(empty) 0 >>> len(singleton) 1 >>> singleton ('hello',)
This is happening because when you save a value like cc
with only one value, it is just saved as an int
and is no longer a tuple, which means it does not have a len()
function. 之所以发生这种情况,是因为当您仅使用一个值来保存
cc
值时,它仅被保存为一个int
且不再是一个元组,这意味着它没有len()
函数。 You can just add a check of the value's type
, such as: 您可以仅添加值
type
的检查,例如:
if type(d[key]) == int:
print(1)
else:
print(len(d[key]))
This way, you will not try to access the length property of an int
, and will not get your error. 这样,您将不会尝试访问
int
的length属性,也不会收到错误。
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