用Python来添加键到dict

Question

I want to add a key with a count one and increment it everytime it increases, this is a classic operation. This is my regular code.

d = OrderedDict()
for i, v in enumerate(s):
   if v not in d:
      d[v] = 1
   else:
      d[v] += 1

How can I do this with 1 line of code using setdefault and not collections. Counter collections. Counter Like if this was a list then I could have done,

d.setdefault(v, []).append()

Is there a way to do a similar thing with integer addition.

Answer 1

你可以这样做：

d[v] = d.get(v, 0) + 1

Answer 2

Just use an ordered counter. If you are happy to import OrderedDict , there's no reason, in my opinion, you should avoid Counter .

from collections import OrderedDict, Counter

class OrderedCounter(Counter, OrderedDict):
    pass

s = [3, 1, 3, 1, 2, 3, 4]

d = OrderedCounter(s)

print(d)

OrderedCounter({3: 3, 1: 2, 2: 1, 4: 1})

Note in Python 3.7+ you can just use Counter since dictionaries are insertion-ordered.

Answer 3

If we want to go for the oneliner and are allowed to use itertools :

import itertools

s = [1, 2, 3, 4, 5, 6, 7, 12, 4, 7, 3]

d = {key: len(list(items)) for key, items in itertools.groupby(sorted(s))}