[Tut] How to Create a Dictionary from two Lists

[Tut] How to Create a Dictionary from two Lists - Printable Version

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[Tut] How to Create a Dictionary from two Lists - xSicKxBot - 04-27-2022

How to Create a Dictionary from two Lists

In this article, you’ll learn how to create a Dictionary from two (2) Lists in Python.

To make it more fun, we have the following running scenario:

Biogenix, a Lab Supplies company, needs to determine the best element from the Periodic Table for producing a new product. They have two (2) lists. The Element Name, the other Atomic Mass. They would prefer this in a Dictionary format.

For simplicity, this article uses 10 of the 118 elements in the Periodic Table.

Question: How would we create a Dictionary from two (2) Lists?

We can accomplish this task by one of the following options:

Method 1: Use
Code:
dict()
and
Code:
zip()
Method 2: Use Dictionary Comprehension
Method 3: Use Generator Expression with
Code:
dict()
and
Code:
zip()
Method 4: Use Lambda

Method 1: Use dict() and zip()

This method uses

Code:
zip()

to merge two (2) lists into an iterable object and (

Code:
dict()

) to convert it into a Dictionary as key:value pairs.

Code:
el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson']
el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216] merge_lists = zip(el_name, el_atom)
new_dict = dict(merge_lists) for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

Lines [1-2] create two (2) lists containing the Element Name (
Code:
el_name
) and corresponding Atomic Mass (
Code:
el_atom
), respectively.
Line [3] merges the two (2) lists using
Code:
zip()
and converts them into an iterable object. The results save to
Code:
merge_lists
.
Line [4] converts
Code:
merge_lists
into a Dictionary (
Code:
dict())
. The results save to
Code:
new_dict
as key:value pairs.
Line [5] instantiates a For loop to return the key:value pairs from
Code:
new_dict
.
- Each iteration outputs the key:value pair in a column format to the terminal.

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182

Method 2: Use Dictionary Comprehension

This method uses https://blog.finxter.com/zip-unzip-python/Dictionary Comprehension to merge two (2) lists into an iterable object and convert it into a Dictionary as key:value pairs. A great one-liner!

Code:
el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson']
el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216]
new_dict = {el_name[i]: el_atom[i] for i in range(len(el_name))} for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

Lines [1-2] create two (2) lists containing the Element Name (
Code:
el_name
) and the corresponding Atomic Mass (
Code:
el_atom
), respectively.
Line [3] merges the lists as key:value pairs and converts them into a Dictionary. The results save to
Code:
new_dict
.
Line [4] instantiates a For loop to return the key:value pairs from
Code:
new_dict
.
- Each iteration outputs the key:value pair in a column format to the terminal.

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182

Method 3: Use Generator Expression with zip() and dict()

This method uses a Generator Expression to merge two (2) lists
into an iterable object (

Code:
zip()

) and convert it into a Dictionary (

Code:
dict()

) as key:value pairs.

Code:
el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson']
el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216]
gen_exp = dict(((k, v) for k, v in zip(el_name, el_atom))) for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

Lines [1-2] create two (2) lists containing the Element Name (
Code:
el_name
) and the corresponding Atomic Mass (
Code:
el_atom
) respectively.
Line [3] uses a Generator Expression to merge the lists (
Code:
zip()
) and create an iterable object. The object converts into a Dictionary (
Code:
dict()
) and saves back to
Code:
gen_exp
.
Line [5] instantiates a For loop to return the key:value pairs from
Code:
new_dict
.
- Each iteration outputs the key:value pair in a column format to the terminal.

Code:
zip()

) and convert it into a Dictionary (

Code:
dict()

) as key:value pairs.

Code:
el_name = ['Meitnerium', 'Darmstadtium', 'Roentgenium', 'Copernicium', 'Nihonium', 'Flerovium', 'Moscovium', 'Livermorium', 'Tennessine', 'Oganesson']
el_atom = [277.154, 282.166, 282.169, 286.179, 286.182, 290.192, 290.196, 293.205, 294.211, 295.216]
new_dict = dict((lambda n, a: {name: el_atom for name, el_atom in zip(n, a)})(el_name, el_atom)) for k, v in new_dict.items(): print ("{:<20} {:<15}".format(k, v))

Lines [1-2] create two (2) lists containing the Element Name (
Code:
el_name
) and the corresponding Atomic Mass (
Code:
el_atom
) respectively.
Line [3] uses a lambda to merge the lists (
Code:
zip()
) and create an iterable object. The results save to a Dictionary
Code:
new_dict
as key:value pairs.
Line [4] instantiates a For loop to return the key:value pairs from
Code:
new_dict
.
- Each iteration outputs the key:value pair in a column format to the terminal.

Code (snippet)

Meitnerium |
277.154

Darmstadtium |
282.166

Roentgenium |
282.169

Copernicium |
286.179

Nihonium |
286.182

Summary

After reviewing the above methods, we decide that Method 2 is best suited: minimal overhead and no additional functions required.

Problem Solved! Happy Coding!