How do you create an empty list of tuples?

Question

I'm trying to create a new empty list that will contain tuples when calling extend. Here's where I declare the list:

ticketData = list()

And I loop through another list to add tuples to this list:

data = (0, requestor, subject, thetime)
ticketData.extend(data)

When I output the result it shows this:

[0, 'Name', 'Test Subject', '03:31:12']

I need it to be a list of tuples, not just a list so that I can use sqlite's executemany function.

It seems straight forward, but I haven't been able to find an answer on here. Thanks!

extend appends all of the elements of its argument. append appends just a single element. If you want to use extend, you could ticketData.extend([data]), but it's easier to just use append. — abarnert
– abarnert, Commented May 23, 2015 at 2:55

Eric Renouf · Accepted Answer · 2015-05-23 02:53:34Z

15

Just append it to the list, so that the tuple will be added instead of having the elements of the tuple extend the list.

ticketData.append(data)

will add data to the list ticketData

answered May 23, 2015 at 2:53

Eric Renouf

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El Sholz · Accepted Answer · 2018-10-26 11:33:56Z

Although this question has been answered already, I thought it could be useful to know about how to construct an iterable that should contain an empty iterable. In Python, constructors like list(), set(), tuple() etc. take an iterable as input. Hence they iterate through the iterable and somthing like list(tuple()) does not return a list with an empty tuple. Instead the list constructor iterates through the tuples, and since it has no items in it it results in an empty list.

To construct a list that contains an empty tuple do the following:

Instead of my_list = list(tuple()) // returns [] or list()

Do: my_list = [tuple()]

Or: my_list = list([tuple()]) //constructor iterates through the list containing the empty tuple

Analogously, if you want to make a set containing an empty tuple do the following:

Instead of my_set = set(tuple()) // returns set()

Do: my_set = {tuple()}

Or: my_set = set([tuple()]) // constructor iterates through the list, containing the empty tuple

This also applies to other iterables. I am writing this, because I myself have had problems using these constructors to return e.g. a list containing another empty iterable.

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