70.01-List-and-Set-Comprehensions.md

70.01-List-and-Set-Comprehensions.md

usecase

The aim of this page📝is to introduce comprehensions and their use for lists. Comprehensions are

• syntactic sugar
  • readable
  • expressive
  • self-documenting by being close to natural language
• or concise syntax for the description of:
  1. lists
  2. sets
  3. dicts

• 1. list comprehensions: syntax
• 2. set comprehensions

1. list comprehensions: syntax

• it seems to be declarative like SQL is declarative
• the expressino can be any python expression
• usually the produce a items in a new list - this makes it similar to map (there you modify the existing values)

#[expression(item) for item in iterable]
list = ['pavol', 'ignatius', 'benedictus']
lengths = [len(name) for name in list] 

• this is the synonym for the following imperative code

lengths = []
for name in list:
    lengths.append(len(name))

2. set comprehensions

• same syntax, only in curly braces - the example is just an illustrative deduplication of the length of the first 19 integers

from math import factorial
s = {len(str(factorial(x))) for x in range(20)}
type(s)
<class 'set'>
print(s)
{1,2,3,4,5,6,7,8,9,10,11,13,14,15,16,18}