Python :function that takes an iterable argument and generates tuples

Question

I try to do something on python.

I try to write a function that takes an iterable argument and generates tuples of 2 elements:

1. the current iterable element
2. the number of times it has been generated since the beginning

Here is my code

liste = ['a','b','a','a','b']

compte = {}.fromkeys(set(liste),0)
for valeur in liste:
     compte[valeur] += 1

print(compte)

output :

{'b': 2, 'a': 3}

But I want to obtain "a:1" "b:1" "a:2" "a:3" and "b:2"

Thanks for help

Answer 1

Use a generator function.

from collections import defaultdict

def with_running_count(values):
    counts = defaultdict(int)
    for value in values:
        counts[value] += 1
        yield value, counts[value]

>>> print(*with_running_count('abaab'))

('a', 1) ('b', 1) ('a', 2) ('a', 3) ('b', 2)

One advantage of using a generator over the other suggestions is that generators are lazy. That means that you can pass in iterators that return an endless (or very large) data stream, since the generator only consumes the input stream when needed.

# an endless iterator
coin = iter(lambda: random.choice(['heads', 'tails']), None)

# the running count will also be endless        
toss = with_running_count(coin)

>>> next(toss), next(toss), next(toss)
(('tails', 1), ('tails', 2), ('heads', 1))

Answer 2

Your expected result is a list, not a dictionary. A fix to your code would be to use your dict for counting, but appending to a list:

>>> liste = ['a','b','a','a','b']
>>>
>>> compte = dict.fromkeys(liste,0) #Or use a default dict
>>> result = []
>>> for valeur in liste:
...  compte[valeur] += 1
...  result.append((valeur,compte[valeur]))
...
>>> print(result)
[('a', 1), ('b', 1), ('a', 2), ('a', 3), ('b', 2)]