[Python-Dev] transitioning from % to {} formatting (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Sat Oct 3 19:35:29 CEST 2009

Paul Moore wrote:

2009/10/1 Eric Smith <eric at trueblade.com>:

It's tangential, but in the str.format case you don't want to check for just '{asctime}', because you might want '{asctime:%Y-%m-%d}', for example.

But there are ways to delay computing the time until you're sure it's actually being used in the format string, without parsing the format string. Now that I think of it, the same technique could be used with %-formatting: Still tangential, but it seems to me that this discussion has exposed a couple of areas where the logging interface is less than ideal: - The introspection of the format string to delay computing certain items (Eric's suggestion may be an improvement here). - The "call str() on any non-string object to get a format string" API (which precludes string subclasses).

Calling str on non-string objects to get a format string does not (prima-facie) preclude string subclasses:

class X(str): pass ... class Y(object): ... def str(self): ... return X('foo') ... a = Y() type(str(a)) <class '__main__.X'>

Michael

I suspect other APIs will exist with similar issues once the whole question of supporting multiple format syntaxes gets wider publicity...

Paul.

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