Are there dictionary comprehensions in Python? (Problem with function returning dict)

I know about list comprehensions, what about dictionary comprehensions?

Expected Output:

>>> countChar('google')
{'e': 1, 'g': 2, 'l': 1, 'o': 2}
>>> countLetters('apple')
{'a': 1, 'e': 1, 'l': 1, 'p': 2}
>>> countLetters('')
{}

Code (I'm a beginner):

def countChar(word):
l = []
#get a list from word
for c  in word: l.append(c)
sortedList = sorted(l)
uniqueSet = set(sortedList)
return {item:word.count(item) for item in uniqueSet }

What is the problem with this code? Why do I get this

SyntaxError

?

return { item:word.count(item) for item in uniqueSet }
^
SyntaxError: invalid syntax

python dictionary python-2.x

edit: As agf pointed out in comments and the other answer, there is a dictionary comprehension for Python 2.7 or newer.

def countChar(word):
return dict((item, word.count(item)) for item in set(word))

>>> countChar('google')
{'e': 1, 'g': 2, 'o': 2, 'l': 1}
>>> countChar('apple')
{'a': 1, 'p': 2, 'e': 1, 'l': 1}

There is no need to convert

word

to
a list or sort it before turning it into a set since strings are iterable:

>>> set('google')
set(['e', 'o', 'g', 'l'])

There is no dictionary comprehension with for Python 2.6 and below, which could be why you are seeing the syntax error. The alternative is to create a list of key-value tuples using a comprehension or generator and passing that into the

dict()

built-in.

If you're on Python 2.7 or newer:

{item: word.count(item) for item in set(word)}

works fine. You don't need to sort the list before you set it. You also don't need to turn the word into a list. Also, you're on a new enough Python to use

collections.Counter(word)

instead.

If you're on an older version of Python, you can't use

dict

comprehensions,
you need to use a generator expression with the

dict

constructor:

dict((item, word.count(item)) for item in set(word))

This still requires you to iterate over

word

len(set(word))

times,
so try something like:

from collections import defaultdict
def Counter(iterable):
frequencies = defaultdict(int)
for item in iterable:
frequencies[item] += 1
return frequencies