Counting entries with Python dictionary datatype

I'm learning Python and writing a program that keeps track of the total number of vari开发者_Go百科ous types of file extensions. I think a dictionary would be the perfect data type to track this information, something like:

.txt  14
.c    27
.java 12

I have some code written that builds a set, which eliminates duplicate file extensions, but how would I use a dictionary in Python to do the same thing but keep track of the number of occurances?

ext_list = set()
for i in file_list:
    ext_list.add(i.extension)

---

In Python 2.7 or above, you can use collections.Counter:

from collections import Counter
c = Counter(i.extension for i in file_list)
print(c)

Counter is a class derived from the standard Python dict.

If you prefer to use a plain dict, you can take advantage of its setdefault() method:

counts = {}
for i in file_list:
    counts.setdefault(i.extension, 0)
    counts[i.extension] += 1

---

ext_count = collections.defaultdict(int)
for i in file_list:
  ext_count[i.extension] += 1