Dictionary comprehension is a concise and powerful way of creating dictionaries in Python. It allows us to create dictionaries in a single line of code, without the need for a loop or multiple lines of code.
In this blog post, we will discuss what dictionary comprehension is and how to use it in Python.
What is Dictionary Comprehension?
Dictionary comprehension is a way of creating dictionaries using a single line of code. It is similar to list comprehension, but instead of creating a list, we create a dictionary.
Dictionary comprehension follows the same syntax as list comprehension, with the difference being that we use curly braces {} instead of square brackets []. The general syntax for dictionary comprehension is:
{key: value for (key, value) in iterable}
Here, key and value represent the key-value pairs that we want to add to the dictionary. iterable can be any iterable object like a list, tuple, or set, which contains the key-value pairs.
For example, let's create a dictionary using a for loop:
my_dict = {}
for i in range(1, 6):
my_dict[i] = i**2
print(my_dict) # Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
Using dictionary comprehension, we can create the same dictionary in a single line of code:
my_dict = {i: i**2 for i in range(1, 6)}
print(my_dict) # Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
As you can see, the syntax for dictionary comprehension is much more concise and readable than using a for loop.
Conditions in Dictionary Comprehension
We can also add conditions in dictionary comprehension to filter out certain key-value pairs based on a condition. The general syntax for adding a condition is:
{key: value for (key, value) in iterable if condition}
Here, condition is the condition that we want to apply to filter the key-value pairs.
For example, let's create a dictionary of even squares:
my_dict = {i: i**2 for i in range(1, 11) if i%2 == 0}
print(my_dict) # Output: {2: 4, 4: 16, 6: 36, 8: 64, 10: 100}
Here, we have added a condition if i%2 == 0 to filter out the odd values and create a dictionary of even squares.
Nested Dictionary Comprehension
We can also create nested dictionaries using dictionary comprehension. The syntax for creating a nested dictionary is:
{outer_key: {inner_key: value for (inner_key, value) in iterable} for (outer_key, iterable) in outer_iterable}
Here, outer_key is the key for the outer dictionary, and inner_key is the key for the inner dictionary. iterable is the iterable containing the inner key-value pairs, and outer_iterable is the iterable containing the outer key-value pairs.
For example, let's create a nested dictionary of even and odd squares:
my_dict = {i: {j: j**2 for j in range(1, i+1) if j%2 == 0} for i in range(2, 6)}
print(my_dict) # Output: {2: {2: 4}, 3: {2: 4}, 4: {2: 4, 4: 16}, 5: {2: 4, 4: 16}}
Here, we have created a nested dictionary of even and odd squares. The outer dictionary has keys 2, 3, 4, and 5, and each key has a nested dictionary containing even squares.
Conclusion
Dictionary comprehension is a powerful and concise way of creating dictionaries in Python. It allows us to create dictionaries in a single line of code, without the need for loops or multiple lines of code. We can also add conditions and create nested dictionaries using dictionary comprehension. By using dictionary comprehension, we can write more readable and maintainable code.
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