insert data from two lists to dict with for loop

Question

I tried this:

numbers_dict = dict()
num_list = [1,2,3,4]
name_list = ["one","two","three","four"]
numbers_dict[name for name in name_list] = num for num in num_list

And as a result I got this exception:

File "<stdin>", line 1
numbers_dict[name for name in name_list] = num for num in num_list

Do you need to handle the case where the lists differ in length? — Two-Bit Alchemist, Jul 03 '18 at 16:07
Another option that's appropriate here: `{name: num for num, name in enumerate(name_list, 1)}` — PM 2Ring, Jul 04 '18 at 10:26

fordy · Accepted Answer · 2018-07-03T22:42:16.037

7

You don't need to explicitly loop. You can use zip to join your two lists and then wrap it in a dict for the result you're looking for:

>>> dict(zip(num_list, name_list))

{1: 'one', 2: 'two', 3: 'three', 4: 'four'}

edited Jul 03 '18 at 22:42

answered Jul 03 '18 at 16:06

fordy

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jpp · Answer 2 · 2018-07-03T16:13:03.027

You are trying to mix list comprehensions, for loops and multiple key access into a single expression. This, unfortunately, is not possible in Python. Choose one method and stick with it.

Here are some options. They all involve zip, which returns elements from each argument iterable sequentially.

for loop

d = {}
for k, v in zip(name_list, num_list):
    d[k] = v

dictionary comprehension

d = {k: v for k, v in zip(name_list, num_list)

dict constructor

d = dict(zip(name_list, num_list))

score 2 · Answer 3 · answered Jul 03 '18 at 16:09

Use zip - https://www.programiz.com/python-programming/methods/built-in/zip.

numbers_dict = dict()
num_list = [1,2,3,4]
name_list = ["one","two","three","four"]

numbers_dict = dict(zip(name_list, num_list))

then print(numbers_dict) gives {'one': 1, 'two': 2, 'three': 3, 'four': 4}.

Lodi · Answer 4 · 2018-07-03T16:26:37.973

2

You NEED to use the For Loop? So just:

for i in range(len(num_list)):
    numbers_dict[num_list[i] = name_list[i]]

But the best tool you could use is zip:

numbers_dict = zip(num_list, name_list)

edited Jul 03 '18 at 16:26

answered Jul 03 '18 at 16:09

Lodi

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In this case also `num_list` can itself be expressed as `range(1, 5)`, simplifying your construct some. – Two-Bit Alchemist Jul 03 '18 at 16:10
1

I totally agree with you, but I'm just complementing OP's answer. – Lodi Jul 03 '18 at 16:11

score 1 · Answer 5 · answered Jul 03 '18 at 16:06

There are comprehensions for dict as well as for list. The dict ones look like the literal syntax:

{key: value for key, value in iterable}

In your case zip is probably the right tool:

>>> num_list = range(1, 5)
>>> name_list = ['one', 'two', 'three', 'four']
>>> zip(num_list, name_list)
[(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
>>> dict(_)
{1: 'one', 2: 'two', 3: 'three', 4: 'four'}

score 1 · Answer 6 · answered Jul 03 '18 at 16:15

1

You can also use pandas:

numbers_series = pd.Series(name_list,index=num_list)

A pandas series acts much like a dictionary, but if you really want it in dictionary form, you can do numbers_dict = dict(numbers_series).

answered Jul 03 '18 at 16:15

Acccumulation

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And you could use a thermonuclear device to kill mosquitoes. :) Pandas is fine when the OP is asking for a Pandas solution, or if they have a lot of data to process, but it's overkill when the OP just wants to turn a pair of small lists into a dict. – PM 2Ring Jul 04 '18 at 10:23

insert data from two lists to dict with for loop

6 Answers6

for loop

dictionary comprehension

dict constructor