How merge a dict and a list and adding more value to it?

Question

we have this dict and this list

mydict={a:1,b:1}
mylist=[a,b,a,c]

I want to merge that list into the dict like this:

mydict={a:3,b:2,c:1}

Answer 1

You can do it by

for item in mylist:
    try:
        mydict[item] += 1
    except KeyError:
        mydict[item] = 1

Answer 2

I would use Counters for this.

from collections import Counter

mydict={'a':1,'b':1}
mylist=['a','b','a','c']

c1 = Counter(mydict)
c2 = Counter(mylist)

mynewdict = c1 + c2

Counter({'a': 3, 'b': 2, 'c': 1})

If you need the newdict as an actual dict and not a counter then:

mynewdict = dict(mynewdict)

Answer 3

A companion to @meTchaikovsky's answer.

for item in mylist:
    mydict[item] = mydict.get(item, 0) + 1