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Description:

PhysicalTurtle 0.4

Physical Turtle
This is an extension for the Python turtle module that provides a
physical space for a turtle to inhabit. The initial aim is to provide
areas of solid space that the turtle cannot move into.
The Turtle class is extended with the following methods. This list
may change as the first version of this package is developed.
Generally, methods are used here rather than attributes to be
consistent with the rest of the Turtle interface.
Methods:

touch_left(), touch_right(), touch_front(), touch_back()
Each one returns True if the Turtle would not be able to move in
that direction.

last_distance()
The distance travelled in the preceding forward or backward
movement. Since the turtle is not able to move through a solid area
this distance may be less than the distance originally called for.

pen_set_solid()
Set a pen property so that any movement of the turtle with the pen
down creates a solid area. The pen colour is not affected, so that
the lines shown on the screen correspond to lines of solidity in
the physical space.
The solid area created by the turtle move is a rectangle
corresponding to the length of the move and the width of the pen.
No solid area is drawn in the pen is up.
The action of filling a polygon with a colour does not create solid
space.

pen_unset_solid()
Reverses the action of pen_set_solid so that turtle movement does
not create solid areas.

The extension provides a new rule that says a turtle cannot cross a
line that has been drawn with pen_set_solid. The turtle is allowed
to move up to the solid line and the attribute last_distance
gives the distance actually moved.
There are two exceptions to this rule:

A turtle with pen up is allowed to move anywhere. This is allows
the turtle to move to any place on the screen and is required for
placing the turtle into an enclosed space.
A turtle with pen solid is allowed to move anywhere. This is
specifically designed to allow drawing a solid shape where one edge
must be drawn contiguously with another. (If this was not allowed,
the second line would not be drawn because it would be trapped by
the end of the first line.)

Installation
Get the version straight from the Python Package Index:
pip install physicalturtle
Or Get the latest version from Bit Bucket:
https://bitbucket.org/mikedeplume/physical-turtle
If you do download the repository, don’t forget to put the
physicalturtle package on your PYTHON_PATH. The easiest way to do
this is to go into the directory and type:
python setup.py install

License
The package uses the MIT license:

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the “Software”), to deal in the Software without
restriction, including without limitation the rights to use, copy,
modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.

Use
The package is intended as a one for one replacement for the built in
turtle module. Any existing turtle software that you have should work
just as before if you replace:
from turtle import ...
with:
from physicalturtle import ...
From that perspective, there is nothing much new to learn.

Examples
These examples can be run either by importing the run procedure or by
executing them from the command line:
$python path/to/package/example_xxx.py
Using the command line is probably going to be appropriate if you have
downloaded the source and want to study how it works.

Random action
At the Python prompt:
>>> from physical_turtle.example_random import run_me
>>> run_me()
And watch the turtle bounce randomly around an enclosed space.

Follow an Outline
At the Python prompt:
>>> from physicalturtle.example_follow import
>>> run_me()
And watch the blue line work its way around the solid object.

A Constrained Random Walk
At the Python prompt:
>>> from physicalturtle.example_walk import run_ahead, run_behind
>>> run_ahead()
>>> run_behind()
This example draws a random walk using a solid line, which means that
the turtle cannot cross its own trail. The drawing rules mean that,
to achieve this, the turtle must switch between a solid line and a
not-solid line. The example shows two ways to do this.

Change History

Version 0.4
Resolve

Issue #1: Solid lines are drawn even when pen is up
Issue #2: Solid lines drawn using goto(x,y) are positioned wrongly.
Issue #3: Follow an object outline losses contact with the object.

Version 0.3
Start making changes for Python 3. The Python 3 turtle module differs
slightly from the Python 2 version (see Python 3 documentation) and
these differences have been reflected in Physical Turtle.
Change the package name to physicalturtle. This is more PEP8ish and
helps to keep some consistency with the PYPI package name. My
apologies to current users for the inconvenience. I realise it will
be inconvenient, but the hit now will save annoyance further down the
line.

Version 0.2
The touch_xxx methods now work. This is illustrated in a new
example, example_follow.py.
The internal mechanism for finishing off the line clipping algorithm
has been tidied up.
The internal mechanisms now distinguish properly between the effective
size of the turtle, the safety_radius, as used in line clipping, and
the reach of the touch_xxx methods, the stick length.

Version 0.1
An initial version focusing on the straight line geometry.