None in string formatting

[Steve Holden]

Jorge Godoy wrote:
> rodney.maxwell at gmail.com writes:
> 
> 
>>Was doing some string formatting, noticed the following:
>>
>>
>>>>>x = None
>>>>>"%s" % x
>>
>>'None'
>>
>>Is there a reason it maps to 'None'? I had expected ''.
> 
> 
> How would know, then, if there was no value at all or if it was an empty
> string? 
> 
Well, for that matter, how can you tell the difference between

'%s' % False

and

'%s' % 'False'

since both inevitably produce the same output.

The bottom line is that you are trying to map the strings plus other 
values on to the strings, which means it's a mathematical certainty 
there will be ambiguities. It's just that you want *your* preferred 
ambiguities rather than what Python gives you.

Suppose Python were to do what you want, how could you distinguish 
between the outputs for "" and None? Of course, at the moment the 
outputs for "None" and None are the same, but that just supports my 
assertion about the inevitability of ambiguities.

regards
  Steve