Day 08 - Comprehensions¶
The Python Comprehensions allow us in a clear and simple way, create sequences from other sequences, these work in a similar way to the filter and map functions.
Types of compressions:
- list comprehensions
- dictionary comprehensions
- set comprehensions
List Comprehensions¶
We can create lists in a clear way, the list comprehension structure is:
new_list = [output for i in sequence if condition]
Almost all the comprehensions work in a similar way depending on the type of structure we need to obtain.
new_list: The variable which will contain the list.output: The output of every element in the list.i: Value in the sequence.condition: (optional) Comprehensions can have conditions to decide which value it will keep.
Common Example¶
totals = []
for number in range(1, 6):
totals.append(number * 2)
print(totals)
We can perform this same action with the map function as we saw before, however this time we will use comprehension:
totals = [number * 2 for number in range(1, 6)]
print(totals)
# Output:
# [2, 4, 6, 8, 10]
It works exactly the same, now how about filtering out just odd numbers?
Remember that we can add a conditional, if it is satisfied, the value will be kept in the new sequence
totals = [number * 2 for number in range(1, 6) if number % 2 != 0]
print(totals)
# Output:
# [2, 6, 10] -> 1, 3, 5 (odd numbers)
Dict Comprehensions¶
They work in a similar way, we just have to take into account, the type of braces that are used and the format of the dictionaries key: value
new_dict = {output_key: output_value for i in sequence if condition}
We will use a list of numbers and create a dictionary in which its key will be the real number and its value will be the number multiplied by itself.
new_dict = {}
numbers = [5, 8, 2, 6, 3]
for number in numbers:
new_dict[number] = number * number
print(new_dict)
# Output:
# {5: 25, 8: 64, 2: 4, 6: 36, 3: 9}
Comprehension¶
numbers = [5, 8, 2, 6, 3]
new_dict = {number: number * number for number in numbers}
print(new_dict)
# Output:
# {5: 25, 8: 64, 2: 4, 6: 36, 3: 9}
In this example we can also use conditionals, the same way we can work with other types of data such as sets or generators.