one-element tuples [Was: Most probably a stupid question, but I still want to ask]

[MRAB]

On 2016-04-11 01:13, Fillmore wrote:
>
> Sorry guys. It was not my intention to piss off anyone...just trying to understand how the languare works
>
> I guess that the answer to my question is: there is no such thing as a one-element tuple,
> and Python will automatically convert a one-element tuple to a string... hence the
> behavior I observed is explained...
>
>   >>> a = ('hello','bonjour')
>   >>> b = ('hello')
>   >>> b
> 'hello'
>   >>> a
> ('hello', 'bonjour')
>   >>>
>
>
> Did I get this right this time?
>
Nope. :-)

A one-element tuple can be written as:

 >>> ('hello',)
('hello',)

As has been said already, it's the comma that makes the tuple. The 
parentheses are often needed to avoid ambiguity.

For example, object are passed into a function thus:

     f(x, y)

(In reality, it's making a tuple and then passing that in.)

What if you want to pass in the tuple (1, 2) as a single argument?

     f((1, 2))

If you write this:

     f(1, 2)

it passes them in as 2 separate arguments.

Or consider this:

    f((1, 2), 3)

This has 2 arguments: the first is the tuple (1, 2) and the second is 
the int 3.

There _is_ one exception though: (). It's the empty tuple (a 0-element 
tuple). It doesn't have a comma and the parentheses are mandatory. 
There's no other way to write it.