PEP 378: Format Specifier for Thousands Separator

[Terry Jan Reedy]

On 5/23/2013 2:42 PM, Dave Angel wrote:
> On 05/23/2013 11:26 AM, Carlos Nepomuceno wrote:

>
>>>>>> eggs(a,f)
>>> Traceback (most recent call last):
>>> File "<pyshell#29>", line 1, in <module>
>>> eggs(a,f)
>>> File "<pyshell#1>", line 1, in eggs
>>> def eggs(spam, ham): return spam % ham
>>> TypeError: not all arguments converted during string formatting
>>>>>> '%s'%(5%3)
>>> '2'
>>
>> So % doesn't handle tuples! Why's that? Is it intentional (by design)?
>>
>
> It's a conflict in the design.  A tuple is used to supply multiple
> arguments to the % operator.  So if you want to have a tuple as the
> first argument, you need to enclose it in another tuple.

The problem is that interpolating 1 to many items into a string is *not* 
a binary operation. The needed hack to pretend that it is, using a tuple 
to represent multiple items rather than just itself, was one of the 
reasons for making string formatting a honest function, where multiple 
items to be formatted are passed as multiple arguments.