Return lists from a list of lists when given an input value

Question

I've been hammering my head for some time over this issue but can't seem find a solution for this, hence I ask for the assistance. PS: still a bit new to programming

I have lists in a list:

[(2012, 'january', 'monday'), (2012, 'february', 'monday'), (2012, 'january', 'tuesday')]

What I want is a new list with lists, when giving in the input "monday':

[(2012, 'january', 'monday'), (2012, 'february', 'monday')]

So far my code:

lists = [(2012, 'january', 'monday'), (2012, 'february', 'monday'), (2012, 'january', 'tuesday')]

day = input("Give day: ") #monday

def select_monday(lists, day):
    list2 = []
    for list in lists:
        if list[2] == day: #from here I'm stuck and do not know how to continue
            list2.append(list[2])
        else:
            return None
    return list2

Result: None

I have no clue how to get all the lists with a certain value

Answer 1

Your code was fine, except, you don't need else statement, because otherwise during next iteration you will loose the results from the previous steps; also you should actually call your function:

lists = [(2012, 'january', 'monday'), (2012, 'february', 'monday'), (2012, 'january', 'tuesday')]

day = input("Give day: ") #monday

def select_monday(lists, day):
    list2 = []
    for list in lists:
        if list[2] == day: #from here I'm stuck and do not know how to continue
            list2.append(list)
    return list2

print(select_monday(lists, day))

And here's a more compact function:

def select_monday_2(lists, day):
    return list(filter(lambda x: x[2] == day, lists))

print(select_monday_2(lists, day))

Answer 2

You return None if the day is not Monday. This works better:

def select_monday(lists, day):
    list2 = []
    for lst in lists:
        if lst[2] == day:
            list2.append(lst)
    return list2

Furthermore, append the whole list, not only the weekday. Finally, better not use list as variable name because it is a built-in.

Now:

>>> select_monday(lists, day)
[(2012, 'january', 'monday'), (2012, 'february', 'monday')]

Shorter alternative, using a list comprehension:

>>> [x for x in lists if x[2] == day]
[(2012, 'january', 'monday'), (2012, 'february', 'monday')]

Answer 3

The problem with this is the else statement. If even one of the checks is false then it will return None . Remove the else statement and get rid of the [2] on the list in the append statement, unless you just want to append the day.

lists = [(2012, 'january', 'monday'), (2012, 'february', 'monday'), (2012, 'january', 'tuesday')]

day = input("Give day: ") #monday

def select_monday(lists, day):
    list2 = []
    for list in lists:
        if list[2] == day: #from here I'm stuck and do not know how to continue
            list2.append(list)
    return list2