Puzzling difference between lists and tuples

[MRAB]

On 2020-09-17 17:47, Ethan Furman wrote:
> On 9/17/20 8:24 AM, William Pearson wrote:
> 
>> I am puzzled by the reason for this difference between lists and tuples.
>> 
>> A list of with multiple strings can be reduced to a list with one string with the expected results:
> 
>> for n in ['first']:
>>      print n
> 
> ['first'] is a list.
> 
>> for n in ('first'):
>>      print n
> 
> ('first') is not a tuple.  The tuple operator is actually the comma:
> 
>   >>> not_a_tuple = ('first')
>   >>> type(not_a_tuple)
> <class 'str'>
> 
>   >>> is_a_tuple = 'first',
>   >>> type(is_a_tuple)
> <class 'tuple'>
> 
> I tend to use both as it makes it stand out a bit more:
> 
>   >>> still_a_tuple = ('first', )
>   >>> type(still_a_tuple)
> <class 'tuple'>
> 
> The only time the parentheses are required for tuple building is when
> they would otherwise not be interpreted that way:
> 
They're needed for the empty tuple, which doesn't have a comma.

> some_func('first', 'second')   # some_func called with two str args
> 
> some_func(('first', 'second')) # some_func called with one tuple arg
>