\section{\module{turtle} ---
         Turtle graphics for Tk}

\declaremodule{standard}{turtle}
   \platform{Tk}
\moduleauthor{Guido van Rossum}{guido@python.org}
\modulesynopsis{An environment for turtle graphics.}

\sectionauthor{Moshe Zadka}{moshez@zadka.site.co.il}


The \module{turtle} module provides turtle graphics primitives, in both an
object-oriented and procedure-oriented ways. Because it uses \module{Tkinter}
for the underlying graphics, it needs a version of python installed with
Tk support.

The procedural interface uses a pen and a canvas which are automagically
created when any of the functions are called.

The \module{turtle} module defines the following functions:

\begin{funcdesc}{degrees}{}
Set angle measurement units to degrees.
\end{funcdesc}

\begin{funcdesc}{radians}{}
Set angle measurement units to radians.
\end{funcdesc}

\begin{funcdesc}{reset}{}
Clear the screen, re-center the pen, and set variables to the default
values.
\end{funcdesc}

\begin{funcdesc}{clear}{}
Clear the screen.
\end{funcdesc}

\begin{funcdesc}{tracer}{flag}
Set tracing on/off (according to whether flag is true or not). Tracing
means line are drawn more slowly, with an animation of an arrow along the 
line.
\end{funcdesc}

\begin{funcdesc}{forward}{distance}
Go forward \var{distance} steps.
\end{funcdesc}

\begin{funcdesc}{backward}{distance}
Go backward \var{distance} steps.
\end{funcdesc}

\begin{funcdesc}{left}{angle}
Turn left \var{angle} units. Units are by default degrees, but can be
set via the \function{degrees()} and \function{radians()} functions.
\end{funcdesc}

\begin{funcdesc}{right}{angle}
Turn right \var{angle} units. Units are by default degrees, but can be
set via the \function{degrees()} and \function{radians()} functions.
\end{funcdesc}

\begin{funcdesc}{up}{}
Move the pen up --- stop drawing.
\end{funcdesc}

\begin{funcdesc}{down}{}
Move the pen down --- draw when moving.
\end{funcdesc}

\begin{funcdesc}{width}{width}
Set the line width to \var{width}.
\end{funcdesc}

\begin{funcdesc}{color}{s}
\funclineni{color}{(r, g, b)}
\funclineni{color}{r, g, b}
Set the pen color.  In the first form, the color is specified as a
Tk color specification as a string.  The second form specifies the
color as a tuple of the RGB values, each in the range [0..1].  For the
third form, the color is specified giving the RGB values as three
separate parameters (each in the range [0..1]).
\end{funcdesc}

\begin{funcdesc}{write}{text\optional{, move}}
Write \var{text} at the current pen position. If \var{move} is true,
the pen is moved to the bottom-right corner of the text. By default,
\var{move} is false.
\end{funcdesc}

\begin{funcdesc}{fill}{flag}
The complete specifications are rather complex, but the recommended 
usage is: call \code{fill(1)} before drawing a path you want to fill,
and call \code{fill(0)} when you finish to draw the path.
\end{funcdesc}

\begin{funcdesc}{circle}{radius\optional{, extent}}
Draw a circle with radius \var{radius} whose center-point is
\var{radius} units left of the turtle.
\var{extent} determines which part of a circle is drawn: if
not given it defaults to a full circle.

If \var{extent} is not a full circle, one endpoint of the arc is the
current pen position. The arc is drawn in a counter clockwise
direction if \var{radius} is positive, otherwise in a clockwise
direction.  In the process, the direction of the turtle is changed
by the amount of the \var{extent}.
\end{funcdesc}

\begin{funcdesc}{goto}{x, y}
\funclineni{goto}{(x, y)}
Go to co-ordinates \var{x}, \var{y}.  The co-ordinates may be
specified either as two separate arguments or as a 2-tuple.
\end{funcdesc}

This module also does \code{from math import *}, so see the
documentation for the \refmodule{math} module for additional constants
and functions useful for turtle graphics.

\begin{funcdesc}{demo}{}
Exercise the module a bit.
\end{funcdesc}

\begin{excdesc}{Error}
Exception raised on any error caught by this module.
\end{excdesc}

For examples, see the code of the \function{demo()} function.

This module defines the following classes:

\begin{classdesc}{Pen}{}
Define a pen. All above functions can be called as a methods on the given
pen. The constructor automatically creates a canvas do be drawn on.
\end{classdesc}

\begin{classdesc}{RawPen}{canvas}
Define a pen which draws on a canvas \var{canvas}. This is useful if 
you want to use the module to create graphics in a ``real'' program.
\end{classdesc}

\subsection{Pen and RawPen Objects \label{pen-rawpen-objects}}

\class{Pen} and \class{RawPen} objects have all the global functions
described above, except for \function{demo()} as methods, which
manipulate the given pen.

The only method which is more powerful as a method is
\function{degrees()}.

\begin{methoddesc}{degrees}{\optional{fullcircle}}
\var{fullcircle} is by default 360. This can cause the pen to have any
angular units whatever: give \var{fullcircle} 2*$\pi$ for radians, or
400 for gradians.
\end{methoddesc}