[Tutor] Making a Primary Number List generator

[Oscar Benjamin]

On 14 May 2013 17:11, Marc Tompkins <marc.tompkins at gmail.com> wrote:
>
> The OP expressed some confusion between what a function DOES and what it RETURNS.  It occurs to me that the print() function (or, more generically, ANY print() function - it doesn't have to be Python 3) is a good demonstration.
>
> Our first exposure to print() is very simple: display something on the screen - what could possibly go wrong?  However, print() can redirect its output to files, printers, skywriters, etc. - and sometimes it will be a real question whether print() succeeded in producing any output.  (If your program is trying to write data into a file, you'd probably like to know whether it worked or not.)  So print() - like all functions - has an optional return value, which your program can read to see whether it needs to retry, display an error message, etc.
>
> Again, the return value of print() - e.g. success/failure - is separate from what print() actually prints.


I was surprised by this so I've just tested it and checked the docs;
the print() function does not return anything (i.e. it returns None).

>>> a = print('qwe')
qwe
>>> a
>>> print(a)
None

http://docs.python.org/3/library/functions.html#print


Oscar