# STARTING WITH PYTHON3 – The very beginning – part 6

Journal: uffmm.org,
ISSN 2567-6458, July 20  2019 – May 12, 2020
Email: info@uffmm.org
Author: Gerd Doeben-Henisch
Email:
gerd@doeben-henisch.de

CONTEXT

This is the next step in the python3 programming project. The overall context is still the python Co-Learning project.

SUBJECT

Meanwhile I am beginning to combine elements of the python language with some applied ideas (in the last section the idea of cognitive entropy illustrated with the equalization of strings). In this section I address the idea of a simple 2-dimensional virtual world, how to represent it with python. In later sections I will use this virtual worlds for some ideas of internal representations and some kinds of learning in an artificial actor.

Remark: for a general help-information you can find a lot of helpful text directly on the python.org site: https://www.python.org/doc/.

###### SZENARIO

Motivation

Because we want to introduce step-wise artificial actors which can learn, show some intelligence, and can work in teams, we need a minimal virtual world to start (this virtual world is a placeholder for the real world later if applied to the real world (RW) by sensors and actors). Although there is a big difference between the real world and a virtual world a virtual world is nevertheless very helpful for introducing basic concepts. And, indeed, finally if you are applying to real world data you will not be able to do this without mathematical models which represent virtual structures. You will need lots of mappings between real and virtual and vice versa. Thus from a theoretical point of view any kind of virtual model will do, the question is only how ‘easily’ and how ‘good’ it fits.

Assumptions Virtual World (VW)

1. A 2-dimensional world as a grid together with a world clock CLCK. The clock produces periodic events which can be used to organize a timely order.

2. There is an x and y axis with the root (0,0) in the upper left corner

3. A coordinate (x,y) represents a position.

4. A position can be occupied by (i) nothing or (ii) by an object. Objects can be obstacles, energy objects (= Food), by a virtual executive actor, or even more.

5. Only one object per position is allowed.

6. It is assumed that there are four directions (headings): ‘North (N)’ as -Y, ‘East (E)’ as +X, ‘South (S)’ as +Y, and ‘West (W)’ as -X.

7. Possible movements are always only in one of the main directions from one cell to the adjacent cell. Movements will be blocked by obstacle objects or actor objects.

8. A sequence of movements realizes in the grid a path from one position to the next.

9. The size of the assumed grids is always finite. In a strict finite world the border of the grid blocks a movement. In a finite-infinite world the borders of the grid are connected in a way that the positions in the south lead to the position in the north and the positions in the east lead to the positions in the west, and vice versa. Therefor can a path in an finite-infinite world become infinite.

10. A grid G with its objects O will be configured at the beginning of an experiment. Without the artificial actors all objects are in a static world assumed to be permanent. In a dynamic world there can be a world function f_w inducing changes depending from the world clock.

11. During an experiment possible changes in the world can happen through a world function f_w, if such a function has been defined. The other possible source for changes are artificial actors, which can act and which can ‘die’.

Remark: The basic idea of this kind of a virtual world I have got from a paper from S.W.Wilson from 1994 entitled ZCS: a zeroth level classifier system published in the Journal Evolutionary Computation vol. 2 number 1 pages 1-18. I have used this concept the first time in a lecture in 2012 (URL: https://www.doeben-henisch.de/fh/gbblt/node95.html). Although this concept looks at a first glance very simple, perhaps too simple, it is very powerful and allows very far reaching experiments (perhaps I can show some aspects from this in upcoming posts :-)).

###### ACTOR STORY
1. There is a human executive actor as a user who uses a program as an assisting actor by an interface with inputs and outputs.

2. The program tries to construct a 2D-virtual world in the format of a grid. The program needs the size of the grid as (m,n) = (number of columns, number of rows), which is here assumed by default as equal m=n. After the input the program will show the grid on screen.

3. Then the program will ask for the percentage of obstacles ‘O’ and energy objects (= food) ‘F’ in the world. Randomly the grid will be filled according to these values.

4. Then a finite number of virtual actors will be randomly inserted too. In the first version only one.

POSSIBLE EXTENSIONS

In upcoming versions the following options should be added:

1. Allow multiple objects with free selectable strings for encoding.

2. Allow multiple actors.

3. Allow storage of a world specification with reloading in the beginning instead of editing.

4. Transfer the whole world specification into an object specification. This allows the usage of different worlds in one program.

###### IMPLEMENTATION

vw1b.py

And with separation of support functions in an import module:

vw1c.py

gridHelper.py(The import module)

###### EXERCISES

m=int(input(‘Number of columns (= equal to rows!) of 2D-grid ?’))

The input() command generates as output a string object. If one wants to use as output numbers for follow-up computations one has to convert the string object into an integer object, which can be done with the int() operator.

mx=nmlist(n)

Is the call of the nmlist() function which has been defined before the main source code (see. above)(in another version all these supporting functions will again be stored as an extra import module:

printMX(mx,n)

This self-defined function assumes the existence of a matrix object mx with n=m many columns and rows. One row in the matrix can be addressed with the first index of mx like mx[i]. The ‘i’ gives the number of the row from ‘above’ starting with zero. Thus if the matrix has n-many rows then we have [0,…,n-1] as index numbers. The rows correspond to the y-axis.

mx = [[‘_’ for y in range(n)] for x in range(n)]

This expression is an example of a general programming pattern in python called list comprehension (see for example chapters 14 and 22 of the mentioned book of Mark Lutz in part 1 of this series). List comprehension has the basic idea to apply an arbitrary python expression onto an iteration like y in range(n). In the case of a numeric value n=5 the series goes from 0 to 4. Thus y takes the values from 0 to 4. In the above case we have two iterations, one for y (representing the rows) and one vor x (representing the columns). Thus this construct generates (y,x) pairs of numbers which represent virtual positions and each position is associated with a string value ‘_’. And because these instructions are enclosed in []-brackets will the result be a set of lists embedded in a list. And as you can see, it works 🙂 But I must confess that from the general idea of list comprehension to this special application is no direct way. I got this idea from the stack overflow web site (https://stackoverflow.com/questions) which offers lots of discussions around this topic.

for i in range(no):

x=rnd.randrange(n)

y=rnd.randrange(n)

mx[x][y]=obj

A simple for-loop to generate random pairs of (x,y) coordinates to place the different objects into the 2D-grid realized as a matrix object mx.

###### Demo

PS C:\Users\gdh\code> python vw1.py

Number of columns (= equal to rows!) of 2D-grid ?5

[‘_’, ‘_’, ‘_’, ‘_’, ‘_’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘_’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘_’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘_’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘_’]

Percentage (as integer) of obstacles in the 2D-grid?45

Number of objects :

11

Position :

3 2

Position :

2 3

Position :

3 2

Position :

3 2

Position :

0 1

Position :

2 2

Position :

0 1

Position :

4 3

Position :

0 2

Position :

3 1

Position :

1 4

New Matrix :

[‘_’, ‘O’, ‘O’, ‘_’, ‘_’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘O’]

[‘_’, ‘_’, ‘O’, ‘O’, ‘_’]

[‘_’, ‘O’, ‘O’, ‘_’, ‘_’]

[‘_’, ‘_’, ‘_’, ‘O’, ‘_’]

Percentage (as integer) of Energy Objects (= Food) in the 2D-grid ?15

Number of objects :

3

Position :

3 4

Position :

0 4

Position :

4 1

New Matrix :

[‘_’, ‘O’, ‘O’, ‘_’, ‘F’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘O’]

[‘_’, ‘_’, ‘O’, ‘O’, ‘_’]

[‘_’, ‘O’, ‘O’, ‘_’, ‘F’]

[‘_’, ‘F’, ‘_’, ‘O’, ‘_’]

Default random placement of one virtual actor

Position :

2 2

New Matrix :

[‘_’, ‘O’, ‘O’, ‘_’, ‘F’]

[‘_’, ‘_’, ‘_’, ‘_’, ‘O’]

[‘_’, ‘_’, ‘A’, ‘O’, ‘_’]

[‘_’, ‘O’, ‘O’, ‘_’, ‘F’]

[‘_’, ‘F’, ‘_’, ‘O’, ‘_’]

# STARTING WITH PYTHON3 – The very beginning – part 2

Journal: uffmm.org,
ISSN 2567-6458, July 9, 2019
Email: info@uffmm.org
Author: Gerd Doeben-Henisch
Email:
gerd@doeben-henisch.de

CONTEXT

This is the next step in the python3 programming project. The first step can be found here. The overall context is still the python Co-Learning project.

PROGRAMMING TOOLS

In this second session we extend the overview of the possible programming tools, how they are interrelated, and how they work.

In the figure above you can see the windows 10 operating system as the root system for everything else. The win10 system communicates with the PATH-variable and uses this information for many operations. How on can edit this variable has been shown in the last session.

One can activate directly from the win10 system the power-shell with a command-line interface. Entering the right code one can activate from the power-shell either directly a python-shell for python commands or one can activate other programs like the editor ‘notepad’ or ‘notepad++’. With such editors one can edit python scripts, store them, and then run these scripts from the power-shell by calling a python-shell with these scripts as arguments (as shown in the first session).

The python shell allows the direct entering of python commands and gives immediately feedback whether it works and how. Therefore one calls this an interactive shell which is very handy to check quickly some commands and their effects.

Another tool, which we will use in this session, is the integrated script environment (IDLE). This is like the python-shell but with some additional functionalities (see below). The main usage is for editing larger python scripts with a built-in editor and for running these scripts.

THE IDLE TOOL

To use this new tool you can press the windows button to see the list of all apps (programs) available on your computer. Under ‘P’ you will find python 3.7.3 and within python you will find an entry for IDLE. By selecting this item and clicking on the right mouse-button you can select the option to attach this icon to the task bar. If it is there you can use it.

If you start the IDLE tool by clicking on the icon from the task bar it opens as a new python interactive shell with some more options.

A first thing you can do is to ask for the actual path you are in. For this you have to import the python module ‘os’ (operating system) and use the command ‘getcwd()‘ from this module. Entering ‘os.getcwd()‘ in the python command line generates the actual path as output on the next line.

>>> import os
>>> os.getcwd()
‘C:\\Users\\gerd_2\\AppData\\Local\\Programs\\Python\\Python37-32’
>>>

This reveals that the actual path is pointing to the location of the python exe module (on my pc). This is not what I want because I have created in the first session a folder with name ‘code’ in my home directory ‘\Users\gerd_2’. From inside of the IDLE tool it is not possible to change the actual path.  But python as language provides lots of options to do this. One option is described below:

The module os offers several functions. Besides the function ‘os.getcwd()’ which we have used already there is another command ‘os.chdir(pathname)‘. But to directly change the actual path one has to be cautious because the path ‘C:\\Users\gerd_2\code‘ includes the ‘\’-sign, this cannot be read directly by the os.chdir() command. You can surround this problem by using the ‘\’-sign twice: first as an ‘escape sign’ and then as the ‘object sign’, resulting in the following command format: ‘C:\\Users\\gerd_2\\code‘. Entering this nothing is given as a result, and when you repeat the question ‘os.getcwd()’ you will receive as new answer the new path. Here the dialog with the python-shell:

Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 21:26:53) [MSC v.1916 32 bit (Intel)] on win32

>>> import os

>>> os.getcwd()

‘C:\\Users\\gerd_2\\AppData\\Local\\Programs\\Python\\Python37-32’

>>> os.chdir(‘C:\\Users\\gerd_2\\code’)

>>> os.getcwd()

‘C:\\Users\\gerd_2\\code’

>>>

You can see that the python command ‘os.getcwd() has been used twice. If you want to repeat some command you can call-back the command history of the python-shell with the keystrokes ‘ALT+P‘. This recalls the past (P) of the command history.

Comment: In the command

>> os.chdir(‘C:\\Users\\gerd_2\\code’)

I have used the back-slash sign ‘\’ twice to make the string fit as argument for the ‘os.chdir()’ command. As one can learn does python allow another solution, which looks like this:

>> os.chdir(r’C:\Users\gerd_2\code’)

The solution is to use an additional ‘r’ directly before the string ‘…’ telling the python interpreter that the following string has to be understood as a raw string. This works, try it out 🙂

IDLE AND EXECUTION OF A SCRIPT

Now if we are in the target folder for my scripts we can look to all files which are in this folder actually. For this we can use the python command ‘os.listdir()’:

>>> os.listdir()

[‘savesrc.txt’, ‘script1.py’, ‘script1.pyw’, ‘script1b.py’, ‘showargs.py’, ‘threenames.py’, ‘tst1.py’, ‘what.py’, ‘what2.py’, ‘__pycache__’]

>>>

You can detect in this list the python script ‘scrpt1.py’. Entering the name of this script either with .py extension or without will not enable an execution:

>>> script1.py

Traceback (most recent call last):

File “<pyshell#6>”, line 1, in <module>

script1.py

NameError: name ‘script1’ is not defined

From the first session we know that we can start the script within the power-shell directly. For this we have to activate the powershell, have to go into the desired folder ‘code’ …

PS C:\Users\gerd_2> cd code

PS C:\Users\gerd_2\code> dir

Verzeichnis: C:\Users\gerd_2\code

Mode LastWriteTime Length Name

—- ————- —— —-

d—– 04.07.2019 19:03 __pycache__

-a—- 01.07.2019 18:44 182 savesrc.txt

-a—- 01.07.2019 18:41 92 script1.py

-a—- 24.06.2019 23:23 126 script1.pyw

-a—- 24.06.2019 22:43 128 script1b.py

-a—- 04.07.2019 18:51 56 showargs.py

-a—- 28.06.2019 00:29 162 threenames.py

-a—- 24.06.2019 21:16 120 tst1.py

-a—- 24.06.2019 22:49 126 what.py

-a—- 24.06.2019 23:56 136 what2.py

… and then we can start the python-script ‘script1.py’:

PS C:\Users\gerd_2\code> python script1.py

win32

1267650600228229401496703205376

pythonpythonpythonpythonpythonpythonpythonpython

PS C:\Users\gerd_2\code>

But because we will here use the IDLE tool we proceed differently. We open the File-Menue to get the desired file script1.py:

Then we load  the python-script script1.py in the editor of the IDLE tool:

and then activate the RUN button for execution:

The script will then be executed and you will see the effect of the execution in the python shell. This looks the same as when you would have called the script within the power-shell calling  the python-shell.

There is still the other option to get the module running by the import command:

>>> import script1.py

win32

1267650600228229401496703205376

pythonpythonpythonpythonpythonpythonpythonpython

Traceback (most recent call last):

File “<pyshell#7>”, line 1, in <module>

import script1.py

ModuleNotFoundError: No module named ‘script1.py’; ‘script1’ is not a package

>>>

The import call works, but at the same time the python-shell states some error, that ‘script1.py’ is not recognized as a true module. This has to be clarified in the next session.

One possible continuation can be found HERE.