Python Dictionary Comprehension

Like List Comprehension, Python allows dictionary comprehensions. We can create dictionaries using simple expressions. A dictionary comprehension takes the form {key: value for (key, value) in iterable}

Python Dictionary Comprehension Example

Here we have two lists named keys and value and we are iterating over them with the help of zip() function.

Python

# Python code to demonstrate dictionary
# comprehension

# Lists to represent keys and values
keys = ['a','b','c','d','e']
values = [1,2,3,4,5]

# but this line shows dict comprehension here
myDict = { k:v for (k,v) in zip(keys, values)}

# We can use below too
# myDict = dict(zip(keys, values))

print (myDict)

Output :

{'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}

Using fromkeys() Method

Here we are using the fromkeys() method that returns a dictionary with specific keys and values.

Python3

dic=dict.fromkeys(range(5), True)

print(dic)

Output:

{0: True, 1: True, 2: True, 3: True, 4: True}

Using dictionary comprehension make dictionary

Example 1:

Python

# Python code to demonstrate dictionary
# creation using list comprehension
myDict = {x: x**2 for x in [1,2,3,4,5]}
print (myDict)

Output :

{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Example 2:

Python

sDict = {x.upper(): x*3 for x in 'coding '}
print (sDict)

Output :

{'O': 'ooo', 'N': 'nnn', 'I': 'iii', 'C': 'ccc', 'D': 'ddd', 'G': 'ggg'}

Using conditional statements in dictionary comprehension

Example 1:

We can use Dictionary comprehensions with if and else statements and with other expressions too. This example below maps the numbers to their cubes that are not divisible by 4.

Python

# Python code to demonstrate dictionary
# comprehension using if.
newdict = {x: x**3 for x in range(10) if x**3 % 4 == 0}
print(newdict)

Output :

{0: 0, 8: 512, 2: 8, 4: 64, 6: 216}

Using nested dictionary comprehension

Here we are trying to create a nested dictionary with the help of dictionary comprehension.

Python3

# given string
l="GFG"

# using dictionary comprehension
dic = {
    x: {y: x + y for y in l} for x in l
}

print(dic)

Output:

{'G': {'G': 'GG', 'F': 'GF'}, 'F': {'G': 'FG', 'F': 'FF'}}