[Python-checkins] python/nondist/peps pep-0295.txt,NONE,1.1

2002年7月22日 13:45:10 -0700

Update of /cvsroot/python/python/nondist/peps
In directory usw-pr-cvs1:/tmp/cvs-serv29263
Added Files:
	pep-0295.txt 
Log Message:
PEP 295, Interpretation of multiline string constants, Koltsov
--- NEW FILE: pep-0295.txt ---
PEP: 295
Title: Interpretation of multiline string constants
Version: $Revision: 1.1 $
Last-Modified: $Date: 2002年07月22日 20:45:07 $
Author: yozh@mx1.ru (Stepan Koltsov)
Status: Draft
Type: Standards Track
Created: 22-Jul-2002
Python-Version: 3.0
Post-History:
Abstract
 This PEP describes an interpretation of multiline string constants
 for Python. It suggests stripping spaces after newlines and
 stripping a newline if it is first character after an opening
 quotation.
Rationale
 This PEP proposes an interpretation of multiline string constants
 in Python. Currently, the value of string constant is all the
 text between quotations, maybe with escape sequences substituted,
 e.g.:
 def f():
 """
 la-la-la
 limona, banana
 """

 def g():
 return "This is \
 string"

 print repr(f.__doc__)
 print repr(g())

 prints:

 '\n\tla-la-la\n\tlimona, banana\n\t'
 'This is \tstring'

 This PEP suggest two things
	- ignore the first character after opening quotation, if it is
	 newline
	- second: ignore in string constants all spaces and tabs up to
	 first non-whitespace character, but no more then current
	 indentation.
 After applying this, previous program will print:

 'la-la-la\nlimona, banana\n'
 'This is string'

 To get this result, previous programs could be rewritten for
 current Python as (note, this gives the same result with new
 strings meaning):

 def f():
 """\
 la-la-la
 limona, banana
 """

 def g():
 "This is \
 string"

 Or stripping can be done with library routines at runtime (as
 pydoc does), but this decreases program readability.
Implementation
 I'll say nothing about CPython, Jython or Python.NET.

 In original Python, there is no info about the current indentation
 (in spaces) at compile time, so space and tab stripping should be
 done at parse time. Currently no flags can be passed to the
 parser in program text (like from __future__ import xxx). I
 suggest enabling or disabling of this feature at Python compile
 time depending of CPP flag Py_PARSE_MULTILINE_STRINGS.
Alternatives
 New interpretation of string constants can be implemented with flags
 'i' and 'o' to string constants, like

 i"""
 SELECT * FROM car
 WHERE model = 'i525'
 """ is in new style,

 o"""SELECT * FROM employee
 WHERE birth < 1982
 """ is in old style, and

 """
 SELECT employee.name, car.name, car.price FROM employee, car
 WHERE employee.salary * 36 > car.price
 """ is in new style after Python-x.y.z and in old style otherwise.

 Also this feature can be disabled if string is raw, i.e. if flag 'r'
 specified.
Copyright
 This document has been placed in the Public Domain.

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