Populating a dictionary using two for loops in Python

Question

I'm trying to create a dictionary using two for loops. Here is my code:

dicts = {}
keys = range(4)
values = ["Hi", "I", "am", "John"]
for i in keys:
    for x in values:
        dicts[i] = x
print(dicts)

This outputs:

{0: 'John', 1: 'John', 2: 'John', 3: 'John'}

Why?

I was planning on making it output:

{0: 'Hi', 1: 'I', 2: 'am', 3: 'John'}

Why doesn't it output that way and how do we make it output correctly?

add a print statement in the second for loop – Ajay May 16 '15 at 21:20 — Ajay, May 16 '15 at 21:20
I tried that the output was still the same – Halcyon Abraham Ramirez May 16 '15 at 21:29 — Halcyon Abraham Ramirez, May 16 '15 at 21:29

score 148 · Accepted Answer · edited Jun 14 '23 at 06:28

148

dicts = {}
keys = range(4)
values = ["Hi", "I", "am", "John"]
for i in keys:
    dicts[i] = values[i]
print(dicts)

alternatively

In [7]: dict(list(enumerate(values)))
Out[7]: {0: 'Hi', 1: 'I', 2: 'am', 3: 'John'}

edited Jun 14 '23 at 06:28

vvvvv

answered May 16 '15 at 21:19

Ajay

2

thank you for your asnwer. thats interesting. because enumerate also gives out numbers right? cool – Halcyon Abraham Ramirez May 16 '15 at 21:32
I'm wondering since your answer has more votes, is there a reason one might prefer your alt answer to the dict(zip()) answer below? Is there any real different in runtime, or since zip is a special type of enumerate does it just come down to whether we want the dict.keys to be integers or strings? – pmackni Jan 18 '21 at 16:24

score 89 · Answer 2 · answered May 16 '15 at 21:20

89

>>> dict(zip(keys, values))
{0: 'Hi', 1: 'I', 2: 'am', 3: 'John'}

answered May 16 '15 at 21:20

17

this looks so simple that I am ashamed of the for loops I did. thank you very much – Halcyon Abraham Ramirez May 16 '15 at 21:33
2

well it does assume that the keys and values are correctly associated by the same indices...I suppose the for loop also assumes this, but it is slightly more flexible – 3pitt Jan 10 '18 at 17:41
1

@MikePalmice: The Python documentation guarantees that this is the case as long as the dictionary is not mutated in between. – Ignacio Vazquez-Abrams Jan 10 '18 at 17:42
Perfect, helped me in my project. Thank you very much, Sir. – Marek Ševela Jun 03 '21 at 14:12

2 Answers2