I-inout.ltx

\documentclass{wsheet}
\usepackage{rcs}
\usepackage{graphics}
\usepackage[colorlinks]{hyperref}
\RCS $Id: I-inout.ltx 239 2010-07-23 21:41:31Z RobPearce $
\RCS $Date: 2010-07-23 22:41:31 +0100 (Fri, 23 Jul 2010) $
\RCS $Revision: 239 $
\sheet{I}{Input and output}
\author{Gareth McCaughan}
\date{Revision \RCSRevision, \RCSDate}
\begin{document}

\section{Credits}

% COPYRIGHT NOTICE:
\copyright{} Gareth McCaughan. All rights reserved.
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This document is part of the LiveWires Python Course. You may
modify and/or distribute this document as long as you comply with the
LiveWires Documentation Licence: you should have received a copy of the
licence when you received this document.

For the \LaTeX{} source of this sheet, and for more information on
LiveWires and on this course, see the LiveWires web site at
\href{http://www.livewires.org.uk/python/}{|http://www.livewires.org.uk/python/|}

%-----------------------------------------------------------------------------
\section{Introduction}

Almost any interesting program has to get information from somewhere,
and produce some sort of answers somewhere. These are called ``input''
and ``output''. This sheet describes some of the ways Python handles
input and output.

Some of the things in here require you to have done

\begin{program}
from livewires import *
\end{program}

before they'll work.

\section{Input}

Here are some useful functions that ask the user a question and
wait for an answer. They all expect that the user will hit
\key{Enter} after typing the answer.

|read_number()| Expects a number. If you type in something that
isn't a number, you'll get told to try again.

|read_number('Enter a number: ')| The same, but prints that message
before waiting for input. It's usually better to use this version
of |read_number| (perhaps with a different message, like |'How old
are you?'|) so that the person using your program knows what's
required.

|read_string()| Expects a string. You don't need to put quotation
marks around it.

|read_string("What's your name?")| Just like |read_string()|, but
prints a message first.

|read_yesorno()| Expects |yes|, |no|, |y| or |n|, in either capitals
or lowercase.

|read_yesorno('Would you like another game?')| Just like
|read_yesorno()|, but prints a message first.

\section{Output}

The main thing you need to know about output is the |print|
statement. It can print any object:

\begin{interaction}
>>> \T{x=[1,2,3]} \C{A list,}
>>> \T{y='zog'}   \C{a string,}
>>> \T{z=99}      \C{a number,}
>>> \T{f=repr}    \C{a function}
>>> \T{print x,y,z,f}
[1, 2, 3] zog 99 <built-in function repr>
\end{interaction}

Notice that it puts spaces between the things it prints.

If you write two |print| statements, one after the other, you'll
see that the second starts printing on a fresh line rather than
following on from the first. If that isn't what you want, put a
comma at the end of the first |print|:

\begin{program}
print 123,
print 456
\end{program}

This will print |123 456| on a single line.
\end{document}