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Date: Sun, 02 Sep 2012 23:43:42 +0100
From: MRAB <python@mrabarnett.plus.com>
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Subject: Re: newbie ``print`` question
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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
 >>>

> Given the input of several posters, I feel like I should probably be
> using the `write` function anyway.   (I don't have a problem pre-
> constructing strings either.)
>
> But I am a newbie, and "all" the show-and-tell examples/tutorials use
> `print`.  But this little thread has helped me a lot.
>