Why isn't a tuple that contains two empty list an empty tuple?

Question

I have a script that basically returns a tuple from a function:

results = some_function()

Then I'm checking to see if there are any results like so:

if results:
   do_something()

This returns True when the tuple has two empty lists. When I use debug mode my results are ([], []). Running len(results) produces a length of 2.

Interestingly, if I do the following:

results = ([])
print(len(results))

It prints 0. Why is that adding another list prints 2?

Should I be overriding the class method __len__ from the function producing the tuple?

`([])` is _not a tuple at all_, it is an empty list written with parens around it. If you want a single-element tuple, add a comma: `([],)`. — RemcoGerlich, Jun 10 '16 at 13:21
@free_mind That is *the* dupe canonical for such posts. See http://stackoverflow.com/questions/linked/12876177. Anyway, Closing as a dupe implies that your question is a good signpost for future readers to view the main question. — Bhargav Rao, Jun 10 '16 at 14:23

score 3 · Accepted Answer · edited Jun 10 '16 at 13:27

3

A tuple is defined by the comma, not the parentheses:

>>> results = ([],)
>>> print(len(results))
1

edited Jun 10 '16 at 13:27

jonrsharpe

115,751
26
228
437

answered Jun 10 '16 at 13:21

Reblochon Masque

35,405
10
55
80

2

absolutely the right answer. `([])`is not the same as `([],)` +1 – Matthias Burger Jun 10 '16 at 13:22
Thanks for your answer, I didn't know this. – nullByteMe Jun 10 '16 at 13:23

Why isn't a tuple that contains two empty list an empty tuple?

1 Answers1