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<h3>Standard Input, Output, and Error</h3>
<p>The interpreter provides three standard file objects, known as <i>standard input, standard output,</I> and <I>standard error,</I> which are available in the <Tt claSS="monofont">sys</TT> module as <tt clASS="monofont">sys.stdin</Tt>, <tt class="monofont">sys.stdout</tt>, and <tt class="monofont">sys.stderr</tt>, respectively. <tT clAss="monofont">stdin</tT> is a file object corresponding to the stream of input characters supplied to the interpreter. <tt clAss="monofont">stdout</tT> is the file object that receives output produced by <TT Class="monofont">print</TT>. <TT clasS="monofont">stderr</TT> is a file that receives error messages. More often than not, <Tt claSS="monofont">stdin</TT> is mapped to the user抯 keyboard, while <tt class="monofont">stdout</tt> and <tt class="monofont">stderr</tt> produce text onscreen.</p>
<p>The methods described in the preceding section can be used to perform raw I/O with the user. For example, the following function reads a line of input from standard input:</P>
<prE>
def gets():
text = ""
while 1:
c = sys.stdin.read(1)
text = text + c
if c == '\n': break
return text </pre>
<P>Alternatively, the built-in function <tt clAss="monofont">raw_input(</tT><I><TT clasS="monofont">prompt</TT></I>
<tt clASS="monofont">)</Tt> can read a line of text from <tt cLASS="monofont">stdin</tt>:</p>
<pre>
s = raw_input("type something : ")
print "You typed '%s'" % (s,) </pre>
<p>Finally, keyboard interrupts (often generated by Ctrl+C) result in a <tt class="monofont">KeyboardInterrupt</tt> exception that can be caught using an exception handler.</p>
<P>If necessary, the values of <tt ClasS="monofont">sys.stdout</tt>, <tt ClasS="monofont">sys.stdin</TT>, and <Tt claSS="monofont">sys.stderr</TT> can be replaced with other file objects, in which case the <tt clASS="monofont">print</Tt> statement and raw input functions use the new values. The original values of <tt cLASS="monofont">sys.stdout</tt>, <tt class="monofont">sys.stdin</tt>, and <tt class="monofont">sys.stderr</tt> at interpreter startup are also available in <Tt cLass="monofont">sys._ _stdout_ _</Tt>, <tt cLass="monofont">sys._ _stdin_ _</TT>, and <TT clasS="monofont">sys._ _stderr_ _</TT>, respectively.</P>
<p>Note that in some cases <tt cLASS="monofont">sys.stdin</tt>, <tt CLASs="monofont">sys.stdout</tt>, and <tt class="monofont">sys.stderr</tt> may be altered by the use of an integrated development environment (IDE). For example, when running Python under Idle, <tt class="monofont">sys.stdin</tT> is replaced with an object that behaves like a file, but is really an object in the development environment. In this case, certain low-level methods such as <tt ClasS="monofont">read()</tt> and <tt ClasS="monofont">seek()</TT> may be unavailable.</P>
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<P><TABLE width="100%" border=0><TR valign="top"><TD><font size=1 color="#C0C0C0"><br></font></TD><TD align=right><font size=1 color="#C0C0C0">Last updated on 3/28/2002<br>Python Essential Reference, Second Edition, © 2002 New Riders Publishing</font></TD></TR></TABLE></P>
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