Marcin Ciura wrote:
> Here is a pre-PEP about print that I wrote recently.
> Please let me know what is the community's opinion on it.
>
> Cheers,
> Marcin
>
>
> PEP: XXX
> Title: Print Without Intervening Space
> Version: $Revision: 0.0 $
> Author: Marcin Ciura <marcin.ciura at polsl.pl>
> Status: Draft
> Type: Standards Track
> Created: 11-Mar-2005
> Post-History: 11-Mar-2005
>
>
> Abstract
>
> This PEP proposes to extend the syntax of the print statement
> so that its space-insertion mechanism can be selectively
> disabled by using double instead of single commas.
>
>
> Rationale
>
> The print statement can write several expressions in one line,
> but presently always separates them with spaces. While this
> behaviour is often desirable, not uncommon are situations, where
> programmers have to use workarounds to achieve a non-spaced
> display. This has been recognized as one of "Python Gotchas"
> [1]. Even the simplest workaround results in an unnecessarily
> complicated code (for the sake of simplicity let us assume that
> fn() returns strings):
>
> result = ''
> for x in seq:
> result += fn(x)
> print result
>
> Not to mention it also has a terrible algorithmic complexity.
> None of the more efficient solutions is particularly
> straightforward, either:
>
> result = []
> for x in seq:
> result.append(fn(x))
> print ''.join(result)
>
> print ''.join([fn(x) for x in seq])
>
> print ''.join(fn(x) for x in seq)
>
> Moreover, all of them require creating one or two temporary
> objects to hold the entire result. If the programmers use one of
> them without qualms, it is only because their mind is warped by
> the limitation of print.
>
> Using write() is not especially appealing either, especially if
> the print statements are used elsewhere in the code:
>
> import sys
> for x in seq:
> sys.stdout.write(fn(x))
> print # or sys.stdout.write('\n')
>
> The proposed extension to the print statement is to use two
> commas to signal that no space should be written after an
> expression:
>
> for x in seq:
> print fn(x),,
> print
>
> To quote "The Zen of Python" [2]: "Beautiful is better than ugly.
> Simple is better than complex. Readability counts."
>
> The proposal applies also to the expressions in the middle of
> the print statement. Thus it provides an alternative to string
> concatenation and string interpolation, either with the '%'-based
> specifiers, or with the '$'-based ones introduced by PEP 292 [3],
> not requiring creating a temporary string object:
>
> print 'The phone number is (',,extension,,')', number,,'.'
>
> Note that I do not claim that the above version is any more
> readable than
>
> print 'The phone number is (%s) %s.' % (extension, number)
>
>
> Specification
>
> It is proposed to allow separating the expressions to be printed
> by single or double commas, and to allow single or double commas
> at the end of the print statement. The two commas shall be
> consecutive, i.e. there shall be no whitespace between them.
> Non-consecutive commas or any sequence of more than two commas
> constitute a syntax error. In the "print chevron" form of the
> statement, the name of the file object shall be separated from
> the next expression only by a single comma, as it is now.
>
> Formally, the proposed syntax of the extended print statement is
>
> print_stmt: "print"
> ( [expression (("," | ",,") expression)* ["," | ",,"]]
> | ">>" expression [(","
> expression (("," | ",,") expression)* ["," | ",,"]]
>
> Implementing the proposed syntax may require introducing a new
> type of token: double comma, or a hack in the parser to recognize
> two consecutive commas in the context of the print statement.
>
> Two new byte codes, parallel to PRINT_ITEM and PRINT_ITEM_TO, are
> needed to implement the semantics of the proposal.
>
>
> Discussion
>
> Pros:
>
> - The proposed semantics allows avoiding temporary string objects
> during the execution of the print statement and often makes for
> more readable and explicit source code.
>
> - The proposed syntax is easy to learn for the beginners.
>
> - It breaks no existing Python code.
>
> - Mistakes are unlikely to happen with the proposed syntax,
> unless someone has problems with his typing or his keyboard,
> in which case any programming is difficult, anyway.
>
> Cons:
>
> - Wrapper functions around print will be unable to mimic its
> syntax. It is, however, impossible even now, due to trailing
> commas.
>
> - In PEP 259 [4], the BDFL has pronounced that he wants to avoid
> any more tinkering with "print".
>
> - PEP 3000 [5] and "Python Regrets" [6] state that the print
> statement is to be replaced with a function in Python 3000,
> so extending it may be a dead path.
>
>
> References
>
> [1] Python Gotchas, Steve Ferg:
> http://www.ferg.org/projects/python_gotchas.html
>
> [2] The Zen of Python, Tim Peters
> http://www.python.org/doc/Humor.html
>
> [3] PEP 292, Simpler String Substitutions, Barry A. Warsaw:
> http://www.python.org/peps/pep-0292.html
>
> [4] PEP 259, Omit printing newline after newline,
> Guido van Rossum:
> http://www.python.org/peps/pep-0259.html
>
> [5] PEP 3000, Python 3.0 Plans, A.M. Kuchling, Brett Cannon:
> http://www.python.org/peps/pep-3000.html
>
> [6] Python Regrets, Guido van Rossum:
> http://www.python.org/doc/essays/ppt/regrets/PythonRegrets.pdf
>
>
> 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
> End:
I also don't miss a no-space option on print. I've always believed
that print statements with commas in them were for simple output with
little or no regard for formatting (like for debugging statements).
If I want precisely formatted output I use '%' formats or I build
the output line manually with joins or some other mechanism. The
''.join(seq) or ''.join([fn(x) for x in seq]) says exactly what
is being done to create the output string. I fail to see why
your proposed solution of:
for x in seq:
print fn(x),,
print
is clearer than:
print ''.join([fn(x) for x in seq])
Also your statement:
print 'The phone number is (',,extension,,')', number,,'.'
requires three double commas and can already be written
more clearly as:
print 'The phone number is ('+extension+') '+number'.'
or even more clearly (as you stated)
print 'The phone number is (%s) %s' % (extension, number)
Just my 2 cents.
Larry Bates
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