Author: guido.van.rossum Date: Tue May 1 01:03:34 2007 New Revision: 55030 Added: peps/trunk/pep-3125.txt (contents, props changed) peps/trunk/pep-3126.txt (contents, props changed) Modified: peps/trunk/pep-0000.txt Log: Two new peps: S 3125 Remove Backslash Continuation Jewett S 3126 Remove Implicit String Concatenation Jewett Modified: peps/trunk/pep-0000.txt ============================================================================== --- peps/trunk/pep-0000.txt (original) +++ peps/trunk/pep-0000.txt Tue May 1 01:03:34 2007 @@ -121,6 +121,8 @@ S 3121 Module Initialization and finalization von Löwis S 3123 Making PyObject_HEAD conform to standard C von Löwis S 3124 Overloading, Generic Functions, Interfaces Eby + S 3125 Remove Backslash Continuation Jewett + S 3126 Remove Implicit String Concatenation Jewett S 3141 A Type Hierarchy for Numbers Yasskin Finished PEPs (done, implemented in Subversion) @@ -484,6 +486,8 @@ SR 3122 Delineation of the main module Cannon S 3123 Making PyObject_HEAD conform to standard C von Löwis S 3124 Overloading, Generic Functions, Interfaces Eby + S 3125 Remove Backslash Continuation Jewett + S 3126 Remove Implicit String Concatenation Jewett S 3141 A Type Hierarchy for Numbers Yasskin Added: peps/trunk/pep-3125.txt ============================================================================== --- (empty file) +++ peps/trunk/pep-3125.txt Tue May 1 01:03:34 2007 @@ -0,0 +1,103 @@ +PEP: 3125 +Title: Remove Backslash Continuation +Version: $Revision$ +Last-Modified: $Date$ +Author: Jim J. Jewett <JimJJewett@gmail.com> +Status: Draft +Type: Standards Track +Content-Type: text/plain +Created: 29-Apr-2007 +Post-History: 29-Apr-2007, 30-Apr-2007 + + +Abstract + + Python initially inherited its parsing from C. While this has + been generally useful, there are some remnants which have been + less useful for python, and should be eliminated. + + This PEP proposes elimination of terminal "\" as a marker for + line continuation. + + +Rationale for Removing Explicit Line Continuation + + A terminal "\" indicates that the logical line is continued on the + following physical line (after whitespace). + + Note that a non-terminal "\" does not have this meaning, even if the + only additional characters are invisible whitespace. (Python depends + heavily on *visible* whitespace at the beginning of a line; it does + not otherwise depend on *invisible* terminal whitespace.) Adding + whitespace after a "\" will typically cause a syntax error rather + than a silent bug, but it still isn't desirable. + + The reason to keep "\" is that occasionally code looks better with + a "\" than with a () pair. + + assert True, ( + "This Paren is goofy") + + But realistically, that parenthesis is no worse than a "\". The + only advantage of "\" is that it is slightly more familiar to users of + C-based languages. These same languages all also support line + continuation with (), so reading code will not be a problem, and + there will be one less rule to learn for people entirely new to + programming. + + +Alternate proposal + + Several people have suggested alternative ways of marking the line + end. Most of these were rejected for not actually simplifying things. + + The one exception was to let any unfished expression signify a line + continuation, possibly in conjunction with increased indentation + + assert True, # comma implies tuple implies continue + "No goofy parens" + + The objections to this are: + + - The amount of whitespace may be contentious; expression + continuation should not be confused with opening a new + suite. + + - The "expression continuation" markers are not as clearly marked + in Python as the grouping punctuation "(), [], {}" marks are. + + "abc" + # Plus needs another operand, so it continues + "def" + + "abc" # String ends an expression, so + + "def" # this is a syntax error. + + - Guido says so. [1] His reasoning is that it may not even be + feasible. (See next reason.) + + - As a technical concern, supporting this would require allowing + INDENT or DEDENT tokens anywhere, or at least in a widely + expanded (and ill-defined) set of locations. While this is + in some sense a concern only for the internal parsing + implementation, it would be a major new source of complexity. [1] + + +References + + [1] PEP 30XZ: Simplified Parsing, van Rossum + http://mail.python.org/pipermail/python-3000/2007-April/007063.html + + +Copyright + + This document has been placed in the public domain. + + + +Local Variables: +mode: indented-text +indent-tabs-mode: nil +sentence-end-double-space: t +fill-column: 70 +coding: utf-8 +End: Added: peps/trunk/pep-3126.txt ============================================================================== --- (empty file) +++ peps/trunk/pep-3126.txt Tue May 1 01:03:34 2007 @@ -0,0 +1,112 @@ +PEP: 3126 +Title: Remove Implicit String Concatenation +Version: $Revision$ +Last-Modified: $Date$ +Author: Jim J. Jewett <JimJJewett@gmail.com> +Status: Draft +Type: Standards Track +Content-Type: text/plain +Created: 29-Apr-2007 +Post-History: 29-Apr-2007, 30-Apr-2007 + + +Abstract + + Python initially inherited its parsing from C. While this has + been generally useful, there are some remnants which have been + less useful for python, and should be eliminated. + + This PEP proposes to eliminate Implicit String concatenation + based on adjacency of literals. + + Instead of + + "abc" "def" == "abcdef" + + authors will need to be explicit, and add the strings + + "abc" + "def" == "abcdef" + + +Rationale for Removing Implicit String Concatenation + + Implicit String concatentation can lead to confusing, or even + silent, errors. + + def f(arg1, arg2=None): pass + + f("abc" "def") # forgot the comma, no warning ... + # silently becomes f("abcdef", None) + + or, using the scons build framework, + + sourceFiles = [ + 'foo.c' + 'bar.c', + #...many lines omitted... + 'q1000x.c'] + + It's a common mistake to leave off a comma, and then scons complains + that it can't find 'foo.cbar.c'. This is pretty bewildering behavior + even if you *are* a Python programmer, and not everyone here is. [1] + + Note that in C, the implicit concatenation is more justified; there + is no other way to join strings without (at least) a function call. + + In Python, strings are objects which support the __add__ operator; + it is possible to write: + + "abc" + "def" + + Because these are literals, this addition can still be optimized + away by the compiler. (The CPython compiler already does. [2]) + + Guido indicated [2] that this change should be handled by PEP, because + there were a few edge cases with other string operators, such as the %. + (Assuming that str % stays -- it may be eliminated in favor of + PEP 3101 -- Advanced String Formatting. [3] [4]) + + The resolution is to treat them the same as today. + + ("abc %s def" + "ghi" % var) # fails like today. + # raises TypeError because of + # precedence. (% before +) + + ("abc" + "def %s ghi" % var) # works like today; precedence makes + # the optimization more difficult to + # recognize, but does not change the + # semantics. + + ("abc %s def" + "ghi") % var # works like today, because of + # precedence: () before % + # CPython compiler can already + # add the literals at compile-time. + + +References + + [1] Implicit String Concatenation, Jewett, Orendorff + http://mail.python.org/pipermail/python-ideas/2007-April/000397.html + + [2] Reminder: Py3k PEPs due by April, Hettinger, van Rossum + http://mail.python.org/pipermail/python-3000/2007-April/006563.html + + [3] PEP 3101, Advanced String Formatting, Talin + http://www.python.org/peps/pep-3101.html + + [4] ps to question Re: Need help completing ABC pep, van Rossum + http://mail.python.org/pipermail/python-3000/2007-April/006737.html + +Copyright + + This document has been placed in the public domain. + + + +Local Variables: +mode: indented-text +indent-tabs-mode: nil +sentence-end-double-space: t +fill-column: 70 +coding: utf-8 +End: