search
Search
Join our weekly DS/ML newsletter layers DS/ML Guides
menu
menu search toc more_vert
Robocat
Guest 0reps
Thanks for the thanks!
close
Comments
Log in or sign up
Cancel
Post
account_circle
Profile
exit_to_app
Sign out
help Ask a question
Share on Twitter
search
keyboard_voice
close
Searching Tips
Search for a recipe:
"Creating a table in MySQL"
Search for an API documentation: "@append"
Search for code: "!dataframe"
Apply a tag filter: "#python"
Useful Shortcuts
/ to open search panel
Esc to close search panel
to navigate between search results
d to clear all current filters
Enter to expand content preview
icon_star
Doc Search
icon_star
Code Search Beta
SORRY NOTHING FOUND!
mic
Start speaking...
Voice search is only supported in Safari and Chrome.
Navigate to
A
A
brightness_medium
share
arrow_backShare
Twitter
Facebook

Python | Dictionary Comprehension

Programming
chevron_right
Python
chevron_right
Operations
chevron_right
Dictionary Operations
chevron_right
Documentation
schedule Jul 1, 2022
Last updated
local_offer Python
Tags

Dictionary comprehension in Python allows us to create a new dictionary in a short, efficient manner.

Syntax

Basic

{key expression: value expression for variable in iterable}

Conditional

{output expression + conditional on output for variable in iterable + conditional on iterable}

Examples

Basic

To create a dictionary with keys 1 ~ 3, and values as 2*key:

doubles = {i: 2*i for i in range(1, 4)}
print(doubles)
{1: 2, 2: 4, 3: 6}

For every element i in the range(1,4), we are adding a key-value pair i: 2*i to the doubles dictionary.

To create a new dictionary d_new by doubling the values of an existing dictionary d_old:

d_old = {'a': 1, 'b': 2, 'c': 3}
d_new = {key:value*2 for (key,value) in d_old.items()}
print(d_new)
{'a': 2, 'b': 4, 'c': 6}

Conditional

Input condition

To specify a condition on the input:

d_old = {'a': 1, 'b': 2, 'c': 3}
d_new = {key:value*2 for (key,value) in d_old.items() if key != 'c'}
print(d_new)
{'a': 2, 'b': 4}

Here, we only loop through (key,value) in the for loop where key does not equal 'c'. Hence, we do not see any key-value pair in the output with key 'c'.

To specify multiple conditions on the input:

d_old = {'a': 1, 'b': 2, 'c': 3}
d_new = {key:value*2 for (key,value) in d_old.items() if key != 'c' if value % 2 == 0}
{'b': 4}

Here we specify two conditions for the input iterable d_old:

1) key must not equal 'c'

2) value must be divisible by 2

Output condition

To specify a condition on the output:

d_old = {'a': 1, 'b': 2, 'c': 3}
d_new = {key:(value*2 if key!='c' else value*3) for (key,value) in d_old.items()}
print(d_new)
{'a': 2, 'b': 4, 'c': 9}

Here, we add key:value*2 to d_new if the key does not equal 'c', otherwise we add key:value*3. Notice how only the value of key 'c' has been multiplied by 3 while the value of keys 'a' and 'b' have only been multiplied by 2.

mail
Join our newsletter for updates on new DS/ML comprehensive guides (spam-free)
robocat
Published by Arthur Yanagisawa
Edited by 0 others
Did you find this page useful?
Ask a question or leave a feedback...
0
thumb_down
0
chat_bubble_outline
0
settings
Enjoy our search
Hit / to insta-search docs and recipes!