CODEWITHSUNDEEP
pythonlisttypesappendtuples
Skywalker326
Skywalker326

Reputation: 1206

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

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

Upvotes: 78

Views: 325505

Answers (5)

Ashwin Reddy
Ashwin Reddy

Reputation: 31

I believe tuple() takes a list as an argument For example,

tuple([1,2,3]) # returns (1,2,3)

see what happens if you wrap your array with brackets

Upvotes: 2

brainless coder
brainless coder

Reputation: 6430

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

Upvotes: 24

BrenBarn
BrenBarn

Reputation: 251383

It has nothing to do with append. tuple(3, 4) all by itself raises that error.

The reason is that, as the error message says, tuple expects an iterable argument. You can make a tuple of the contents of a single object by passing that single object to tuple. You can't make a tuple of two things by passing them as separate arguments.

Just do (3, 4) to make a tuple, as in your first example. There's no reason not to use that simple syntax for writing a tuple.

Upvotes: 2

Bhargav Rao
Bhargav Rao

Reputation: 52071

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

Upvotes: 98

101
101

Reputation: 8999

There should be no difference, but your tuple method is wrong, try:

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

Upvotes: 1

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