PEP 461: more updates

pep-0461.txt

@@ -8,14 +8,25 @@ Type: Standards Track
 Content-Type: text/x-rst
 Created: 2014-01-13
 Python-Version: 3.5
-Post-History: 2014-01-13
+Post-History: 2014-01-14, 2014-01-15
 Resolution: 
 
 
 Abstract
 ========
 
-This PEP proposes adding the % and {} formatting operations from str to bytes.
+This PEP proposes adding the % and {} formatting operations from str to bytes [1].
+
+
+Overriding Principles
+=====================
+
+In order to avoid the problems of auto-conversion and value-generated exceptions,
+all object checking will be done via isinstance, not by values contained in a
+Unicode representation.  In other words::
+
+  - duck-typing to allow/reject entry into a byte-stream
+  - no value generated errors
 
 
 Proposed semantics for bytes formatting
@@ -26,7 +37,7 @@ Proposed semantics for bytes formatting
 
 All the numeric formatting codes (such as %x, %o, %e, %f, %g, etc.)
 will be supported, and will work as they do for str, including the
-padding, justification and other related modifiers.
+padding, justification and other related modifiers, except locale.
 
 Example::
 
@@ -44,13 +55,13 @@ Example:
     >>> b'%c' % b'a'
     b'a'
 
-%s is a restricted in what it will accept::
+%s is restricted in what it will accept::
 
   - input type supports Py_buffer?
     use it to collect the necessary bytes
 
   - input type is something else?
-    use its __bytes__ method; if there isn't one, raise an exception [3]
+    use its __bytes__ method; if there isn't one, raise an exception [2]
 
 Examples:
 
@@ -76,23 +87,49 @@ Examples:
 
       'a string'.encode('latin-1')
 
-Unsupported % format codes
-^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-%r (which calls __repr__) is not supported
-
-
 format
 ------
 
-The format mini language will be used as-is, with the behaviors as listed
-for %-interpolation.
+The format mini language codes, where they correspond with the %-interpolation codes,
+will be used as-is, with three exceptions::
+
+  - !s is not supported, as {} can mean the default for both str and bytes, in both
+    Py2 and Py3.
+  - !b is supported, and new Py3k code can use it to be explicit.
+  - no other __format__ method will be called.
+
+Numeric Format Codes
+--------------------
+
+To properly handle int and float subclasses, int(), index(), and float() will be called on the
+objects intended for (d, i, u), (b, o, x, X), and (e, E, f, F, g, G).
+
+Unsupported codes
+-----------------
+
+%r (which calls __repr__), and %a (which calls ascii() on __repr__) are not supported.
+
+!r and !a are not supported.
+
+The n integer and float format code is not supported.
 
 
 Open Questions
 ==============
 
-Do we need no support all the numeric format codes?  The floating point
+Currently non-numeric objects go through::
+
+  - Py_buffer
+  - __bytes__
+  - failure
+
+Do we want to add a __format_bytes__ method in there?
+
+  - Guaranteed to produce only ascii (as in b'10', not b'\x0a')
+  - Makes more sense than using __bytes__ to produce ascii output
+  - What if an object has both __bytes__ and __format_bytes__?
+
+Do we need to support all the numeric format codes?  The floating point
 exponential formats seem less appropriate, for example.
 
 
@@ -121,15 +158,11 @@ is a str  (b'%s' % 'abc'  --> b"'abc'").
     easily fixed.
 
 
-Foot notes
-==========
+Footnotes
+=========
 
-.. [1] Not sure if this should be the numeric __str__ or the numeric __repr__,
-       or if there's any difference
-.. [2] Any proper numeric class would then have to provide an ascii
-       representation of its value, either via __repr__ or __str__ (whichever
-       we choose in [1]).
-.. [3] TypeError, ValueError, or UnicodeEncodeError?
+.. [1] string.Template is not under consideration.
+.. [2] TypeError, ValueError, or UnicodeEncodeError?
 
 
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