Append a tuple to a list - what's the difference between two ways?

59

I wrote my first "Hello World" 4 months ago. Since then, I have been following a Coursera Python course provided by Rice University. I recently worked on a mini-project involving tuples and lists. There is something strange about adding a tuple into a list for me:

a_list = []
a_list.append((1, 2))       # Succeed! Tuple (1, 2) is appended to a_list
a_list.append(tuple(3, 4))  # Error message: ValueError: expecting Array or iterable

It's quite confusing for me. Why specifying the tuple to be appended by using "tuple(...)" instead of simple "(...)" will cause a ValueError?

BTW: I used CodeSkulptor coding tool used in the course

This question is tagged with python list types append tuples

~ Asked on 2015-07-02 03:43:03

The Best Answer is


72

The tuple function takes only one argument which has to be an iterable

tuple([iterable])

Return a tuple whose items are the same and in the same order as iterable‘s items.

Try making 3,4 an iterable by either using [3,4] (a list) or (3,4) (a tuple)

For example

a_list.append(tuple((3, 4)))

will work

~ Answered on 2015-07-02 03:47:28


19

Because tuple(3, 4) is not the correct syntax to create a tuple. The correct syntax is -

tuple([3, 4])

or

(3, 4)

You can see it from here - https://docs.python.org/2/library/functions.html#tuple

~ Answered on 2015-07-02 03:48:15


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