Append a tuple to a list – what's the difference between two ways?
Question:
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
Answers:
There should be no difference, but your tuple method is wrong, try:
a_list.append(tuple([3, 4]))
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
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.
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
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
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
There should be no difference, but your tuple method is wrong, try:
a_list.append(tuple([3, 4]))
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
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.
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
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