Why the expression "(1)" is not an one-arity tuple, but int ?

[MRAB]

Andre Engels wrote:
> 2009/12/4 Петров Александр <gmdidro at gmail.com>:
>> Hello All !
>>
>> In my code I try to use a generic approach to work with tuples. Let
>> "X" be a tuple.
>> When I want to access a first element of a tuple, I can write: "X[0]".
>> And that is really working when X is a n-arity tuple, with n>1 (for
>> example "foo( (1,2,3) )" ).
>> But when I call my library function with a 1-arity tuple (for example
>> "foo( (1) )" ) I have an error:
>>
>> TypeError: 'int' object is unsubscriptable
>>
>> How could I tell Python that "(1)" is not an integer, but an one-arity tuple ?
> 
> Tuples in Python are recognized/defined not by the brackets, but by
> the commas; the brackets just function to specify the exact beginning
> and ending of the tuple in cases where that is not directly clear.
> "(1,2,3)" is a tuple, but "1,2,3" is also the same tuple. A 1-tuple
> can be created as "1," or "(1,)".
> 
The only exception is the 0-tuple (). No comma.