flatten.py

# Flatten a list
# Write a function that takes a list of lists and flattens it into a one-dimensional list.
# Name your function flatten. It should take a single parameter and return a list.
# For example, calling:
# flatten([[1, 2], [3, 4]])
# Should return the list:

# [1, 2, 3, 4]

#My naive solution
def flatten(l1):
    newlist = []
    for i in l1:
        for x in i:
            newlist.append(x)
    return newlist

#Python principles

# naive solution
def flatten(outer_list):
    result = []
    for inner_list in outer_list:
        for item in inner_list:
            result.append(item)
    return result

# solution with nested list comprehensions
# (can be put on a single line for conciseness)
def flatten(outer_list):
    return [
        item
        for inner_list in outer_list
        for item in inner_list
    ]