Talin wrote:
> Ron Adam wrote:
>> After a fair amount of experimenting today, I think I've found a nice
>> middle ground that meets some of what both you and Guido are looking
>> for. (And a bit my own preference too.)
>
> First off, thank you very much for taking the time to think about this
> in such detail. There are a lot of good ideas here.
Thanks, I use string operations a *lot* and I really do want it to work as
easy as possible in a wide variety of situations.
> What's missing, however, is a description of how all of this interacts
> with the __format__ hook. The problem we are facing right now is
> sometimes we want to override the __format__ hook and sometimes we
> don't. Right now, the model that we want seems to be:
>
> 1) High precedence type coercion, i.e. 'r', which bypasses __format__.
I think you are looking for an internal simplicity which isn't needed, and
most people won't even think about.
The exposed interface doesn't have any ambiguities if 'r' is a format
specification just like 's', 'd', or 'f'. These are what the formatter
will dispatch on. I think a few if/else's to catch types that will call
__repr__ and __str__, instead of __format__ aren't that costly. I think
there are other areas that can be optimized more, and/or other points where
we can hook into and modify the results.
Or am I missing something still? Maybe if you give an example where it
makes a difference it would help us sort it out.
> 2) Check for __format__, and let it interpret the format specifier.
> 3) Regular type coercion, i.e. 'd', 'f' and so on.
> 4) Regular formatting based on type.
The sequence of parsing I have so far.
1. Split string into a dictionary of fields and a list of string parts.
'Partnumber: {0:10}, Price: ${1:f.2}'.format('123abc', 99.95)
Results in...
{'0':('', 10), '1':('f.2', '')} # key:(format_spec, align_spec)
['Partnumber: ', '{0}', ' Price: $', '{1}']
2. Apply the format_spec and then the alignment_spec to the arguments.
{'0':'123abc ', '1':'99.95'}
* If the arguments are a sequence, they are enumerated to get keys.
* If they are a dict, the existing keys are used.
* Passing both *args and **kwds should also work.
3. Replace the keys in the string list with the corresponding formatted
dictionary values.
['Partnumber: ', '123abc ', ' Price: $', '99.95']
4. Join the string parts back together.
'Partnumber: 123abc Price: $99.95'
It may be useful to expose some of these intermediate steps so that we
could pre-process the specifications, or post-process the formatted results
before it gets merged back into the string.
Which seems to fit with some of your thoughts, although I think you are
thinking more in the line of overriding methods instead of directly
accessing the data. A little bit of both could go a long ways.
Cheers,
Ron
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