On 03/09/2012 00:33, gwhite wrote:
On Sep 2, 3:43 pm, MRAB <pyt...@mrabarnett.plus.com> wrote:
On 02/09/2012 21:58, gwhite wrote:
> On Sep 2, 1:16 pm, Dave Angel <d...@davea.name> wrote:
>> On 09/02/2012 03:50 PM, gwhite wrote:
>> > On Sep 2, 12:43 pm, Dave Angel <d...@davea.name> wrote:
>> >> On 09/02/2012 03:34 PM, gwhite wrote:
>> >>> <snip>
>> >>> btw, I also thought the default "add a CR LF" to the end was odd too.
>> >>> But at least that one had a simple way out.
>> >> But it (print on Python 2.x) doesn't, unless you're stuck on Windows.
>> >> And even then, you can prevent it by using a 'b' in the mode.
>> > Yes, I'm using windows. What is "'b' in the mode?" The help for
>> > print says:
>> > A ``'\n'`` character is written at the end, unless the ``print``
>> > statement ends with a comma. This is the only action if the statement
>> > contains just the keyword ``print``.
>> > So I followed with a comma to stop the default CR LF insertion.
>> You're correct; the best way to suppress the newline at the end of
>> print is to use the trailing comma. But since print is for lines, it
>> usually is a good default. If you don't want to get any extra
>> characters, just use write(). It takes a string, and outputs exactly
>> what it's given.
>> I assumed you were complaining about the conversion of newline to
>> carriage-return-newline, which is done by default on Windows, and can be
>> suppressed by opening the file with "b" as the mode parameter.
> Sorry, I was a little vague on the newline stuff.
> In any case, I've learned I should probably avoid the comma, if
> looking at 3.x:
>>>> from __future__ import print_function
>>>> print('a=%.1f,' % 1.0),;print('b=%.1f' % 2.0)
> a=1.0,
> (None,)
> b=2.0
Explanation:
With 'print' as a function, the first 'print' prints the result of
"'a=%.1f,' % 1.0" and then returns None. The trailing comma makes that
into a tuple (None,), which is printed by the interactive interpreter
as such.
In other words:
>>> None,
(None,)
>>>
The second prints the result of "'b=%.1f' % 2.0" and then returns None.
The interactive interpreter, recognising that it's only None, doesn't
bother to print it.
In other words:
>>> None
Thanks, that makes sense.
It does look like 2.7 & 3.3 don't parse the comma the same way. Just
to repeat, since I didn't give the exact same line to both versions of
Python:
2.7
print('a=%.1f,' % 1.0),;print('b=%.1f' % 2.0)
a=1.0, b=2.0
This has been more informative than I thought it was going to be.
Basically:
In Python 2, 'print' is a statement.
In Python 3, 'print' is a function.
so they _would_ be parsed differently, because they _are_ different.
However, in later versions of Python 2, such as 2.7, adding "from
__future__ import print_function" will make 'print' a function like in
Python 3. (It has no effect in Python 3 because 'print' is already a
function, of course, so if you've converted a Python 2 script which
contains it to Python 3 and just happened to leave it in, it won't
complain either.)
--
http://mail.python.org/mailman/listinfo/python-list
