Python List to Dictionary conversion via Comprehension

Question

Say I have some function which returns a dictionary and I iterate over that function. This will produce a list of dictionaries. I wish to convert this into a dictionary. I am calling my function like this:

x = [_myfunction(element) for element in list_of_elements]

Resulting in say x:

x = [{'one': {'two':'2'}, 'three' : '3'}, {'four':'five', 'six':{'seven':7}}]

and I wish to convert into y:

y = {'one': {'two':'2'}, 'three' : '3', 'four':'five', 'six':{'seven':7}}

Is there a way of calling _myfunction() over the list_of_elements, such that it directly results in y? Maybe with a dictionary comprehension instead of the above list comprehension? Or what the most concise code to turn x into y. (Hopefully without being boring and using a for loop! :-) )

Thanks, labjunky

Answer 1

You can merge dicts using the dict.update method:

y = {}
for element in list_of_elements:
  y.update(_myfunction(element))

You can also use a (double-loop) dict-comprehension:

y = {
    k:v
    for element in list_of_elements
    for k,v in _myfunction(element).items()
}

Finally, if you take any of the answers to this question, for merging two dicts (and name it merge_dicts), you can use reduce to merge more than two:

dicts = [_myfunction(element) for element in list_of_elements]
y = reduce(merge_dicts, dicts, {})

Either way, in case of repeated dict keys, later keys overwrite earlier ones.