MyList = ["a", "b", "a", "c", "c", "a", "c"]

return my_dict = {i:MyList.count(i) for i in MyList}
# returns :
{'a': 3, 'c': 3, 'b': 1}
 # OR
from collections import Counter
return my_dict = dict(Counter(MyList))
# returns :   
{'a': 3, 'c': 3, 'b': 1}
# the both returns the same so it's up to you to choose the one you prefere ;)

>>> l = ["a","b","b"]
>>> l.count("a")