[Python-Dev] User conversions in custom string.Formatter (original) (raw)

Eric Smith eric at trueblade.com
Wed Mar 16 01:25:22 CET 2011

On 03/15/2011 08:07 PM, Andrew Svetlov wrote:

As PEP 3101 http://www.python.org/dev/peps/pep-3101/ says (and current Python does) user can specify conversions like "{0!s}". In custom formatters (derived from string.Formatter) he can override convertfield method to add custom conversions.

I experimented with that last month and found it very convenient. From my perspective custom conversions are very close to 'filters' from html template engines (jinja2, mako, django etc). While I like to see custom conversions simple and easy I don't wan't to bring 'cascading' and 'parametrization' to standard formatting. But why don't relax spec a bit and allow to use any word (with 'identifier' semantix, I mean str.isidentifier()) as conversion name? Proposed update doesn't make any backward incompatibility (both python and public C API are not changed), it's clean and obvious. And it's very funny to use words instead single characters for custom user-specific conversions. What do you think?

This should be in python-ideas, but I don't know if Andrew is subscribed, so I'll reply here until it gets out of control.

Andrew: Could you give a code sample of what you'd like to see?

Eric.

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