Python: How to add tuple to an empty list?

Question

I've looked around at other posts on here for a solution to my problem but none of them seems to work for me. I want to append a tuple to (what starts out as) an empty list. I've checked my code and it looks like whenever I try to just append my tuple it turns the list into a NoneType object. Here's what I've got:

list_of_pairs = []
for player in standings:
    opponent = standings[standings.index(player) + 1]
    matchup = (player[0:2] + opponent[0:2])
    list_of_pairs = list_of_pairs.append(matchup)
    print "ADDED TO LIST: " + str(list_of_pairs)

Each player in the standings list contains a tuple with four elements. I've tried using index and re-assigning list_of_pairs = [list_of_pairs, matchup], but nothing seems to be returning the right thing (i.e. [(player),(next player), (another player), (etc.)]. Every time I print "added to list" I just get ADDED TO LIST: None. I've checked matchup as well and it's definitely storing the first two values of the respective players fine. Any ideas?

Possible duplicate of Why does append return none in this code? — SiHa
– SiHa, Commented Jun 2, 2016 at 11:31

Farhan.K · Accepted Answer · 2016-06-02 10:52:06Z

1

This is because appending an element to a list returns None, which you are then printing when you do:

list_of_pairs = list_of_pairs.append(matchup)
print "ADDED TO LIST: " + str(list_of_pairs)

For example:

>>> a = []
>>> b = a.append('hello')
>>> print a
['hello']
>>> print b
None

answered Jun 2, 2016 at 10:52

Farhan.K

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4 Comments

zds_cn Over a year ago

yes, it's means you can translate "list_of_pairs = list_of_pairs.append(matchup)" to "list_of_pairs.append(matchup)". then try again.

Dave Over a year ago

So could I get round this by generating a new variable (let's say appended_list), and doing appended_list = list_of_pairs.append(matchup) instead? Would that then mean that list_of_pairs would actually contain the values needed while appended_list would return None?

Dave Over a year ago

Forget the above! I think I just realised what you mean! The problem is that I'm re-assigning the variable to itself when I'm appending it right? So the solution is just list_of_pairs.append(matchup) without list_of_pairs =

Dave Over a year ago

Thanks for this, I literally spent half a day staring at this trying to figure it out!

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