[Python-ideas] format specifier for "not bytes"

[Nick Coghlan]

A couple of people at PyCon Au mentioned running into this kind of issue
with Python 3. It relates to the fact that:
1. String formatting is *coercive* by default
2. Absolutely everything, including bytes objects can be coerced to a
string, due to the repr() fallback

So it's relatively easy to miss a decode or encode operation, and end up
interpolating an unwanted "b" prefix and some quotes.

For existing versions, I think the easiest answer is to craft a regex that
matches bytes object repr's and advise people to check that it *doesn’t*
match their formatted strings in their unit tests.

For 3.4+ a non-coercive string interpolation format code may be desirable.

Cheers,
Nick.

--
Sent from my phone, thus the relative brevity :)
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