read44.md

Reading 8: List Comprehensions in Python

List Comprehensions :

def: "It consists of brackets containing an expression followed by a for clause, then zero or more for or if clauses. The expressions can be anything, meaning you can put in all kinds of objects in lists."

here was a given example and how to make list comprehension:

new_list = []
for i in old_list:
    if filter(i):
        new_list.append(expressions(i))

new_list = [expression(i) for i in old_list if filter(i)]

Mainly : 
we have an existing list that has data then we access the list and do an action (accessing and manipulating) transform it to a new list

another example (Squares):

squares = []
for x in range(10):
squares.append(x**2)

that is the same as :

squares = [x**2 for x in range(10)]

another example (filter):

fh = open("test.txt", "r")
result = [i for i in fh if "line3" in i]
print result

Using list comprehension in functions

Examples on how to use functions :

def double(x):
return x*2
>>> print double(5)
10

>>> [double(x) for x in range(10)]
print double
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
# with conditions:
>>> [double(x) for x in range(10) if x%2==0]
[0, 4, 8, 12, 16]

# with more arguments:

>>> [x+y for x in [10,30,50] for y in [20,40,60]]
[30, 50, 70, 50, 70, 90, 70, 90, 110]

• more examples: https://www.pythonforbeginners.com/basics/list-comprehensions-in-python#htoc-syntax