Is it possible to create a dictionary inside a function using python?

Question

I am trying the following

def myfunction(list_a, list_b, my_dict):
   dict1 = dict(zip(list_a, list_b))
   my_dict = copy.deepcopy(dict1)

but when I call myfunction I get an emtpty dictionary...

Are you calling this function, and expecting the reference you used as the argument `my_dict` to contain the copy? If so, it will not. Parameters are passed by the value of the object reference — James Wierzba, Nov 18 '15 at 22:06
@ Jonathan Clede I need the dictionary that is supposed to be produced by this function — Eleftheria, Nov 18 '15 at 22:13
@James Wierzba you are right! I am quite new to programming.. I had an idea that as I can pass an empty list inside a function and append it that I could do something similar with a dictionary like pass an empty dictionary and fill it somehow inside a function.. thank you for your theoretical support! — Eleftheria, Nov 18 '15 at 22:29

furas · Accepted Answer · 2015-11-18T22:13:22.553

2

def myfunction(list_a, list_b):
   dict1 = dict(zip(list_a, list_b))
   return copy.deepcopy(dict1)

my_dict = myfunction(some_list_a, some_list_b)

as MaxNoe noticed - deepcopy is not needed

def myfunction(list_a, list_b):
   return dict(zip(list_a, list_b))

my_dict = myfunction(some_list_a, some_list_b)

or even

my_dict = dict(zip(some_list_a, some_list_b))

edited Nov 18 '15 at 22:13

answered Nov 18 '15 at 22:03

furas

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Why would you make a deep copy of an object you just created? – MaxNoe Nov 18 '15 at 22:09
thank you! but how can I then have access to the returned dictionary? How do I refer to it? – Eleftheria Nov 18 '15 at 22:12
`my_dict[some_key]`, `my_dict[other_key]`, etc. – furas Nov 18 '15 at 22:14

score 2 · Answer 2 · answered Nov 18 '15 at 22:12

2

If you want to make it a function, you should just simply return the dict. No need to give an dictionary or make a deepcopy:

def dict_from_lists(keys, vals):
    return dict(zip(keys, vals))

my_dict = dict_from_lists(list_a, list_b)

But for one line of code only using builtins, I would normally not write a function.

In my opinion

my_dict = dict(zip(list_a, list_b))

is pythonic, it does not need a user function that hides what is going on.

answered Nov 18 '15 at 22:12

MaxNoe

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I need to make it a lot of times for different lists so I thought to try make a fuction to do it for me for all the times needed – Eleftheria Nov 18 '15 at 22:16

score 0 · Answer 3 · edited Nov 18 '15 at 23:35

0

Objects are passed by value of the reference, so assigning a new value to the parameter within the function will not change the value of the object reference that was passed to it.

I suggest returning the copy instead.

def myfunction(list_a, list_b):
   dict1 = dict(zip(list_a, list_b))
   return copy.deepcopy(dict1)

edited Nov 18 '15 at 23:35

Eleftheria

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answered Nov 18 '15 at 22:08

James Wierzba

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Is it possible to create a dictionary inside a function using python?

3 Answers3