Learning a New Programming Language, with Life (part 3)

I started learning Python three days ago, as described here in part 1 and part 2.

Just two hours a day, and I’m well on my way, because here below is a working implementation of my favorite, Conway’s Game of Life, in Python.

Today I refactored to put instance-specific initializations right in the functions that needed them, and promoted parsing of command line arguments to the main program. (Future: use argparse.)

I also realized that these functions are just procedures, so I stopped trying to return meaningful values. I removed the return statements. Python supports that, and returns None.

Update:

A day later, after questions from a reader led me to review my own code, I wondered why it works even without wraparound for negative indices!

The answer: Python lists handle negative indexes gracefully.

Let’s go to the code …

#Life.py

#Implementation of Conway’s Game of Life
#See https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life

#Tom Harris 22-Jul-2015
#Tom Harris 23-Jul-2015 add multiple generations and display period to main program

#Import libraries needed
import sys #for command line argument support

#Define the Life class

class Life:
….#class attributes
….#None

….#class methods
….#NOTE: Currently all procedures — no return statement, implicitly returns None
….
….def readBoardFromFile(self, filename):
……..#Initialize (clear) the board of Life cells
……..self.mainBoard = []

……..#Open the file
……..initialGenerationFile = open(filename)

……..#Read from the file, line by line:
……..for line in initialGenerationFile:
…………listLine = list(line.rstrip(‘\r\n’))
…………self.mainBoard.append(listLine) #add the line, in Python list format, to the mainBoard

……..#Determine dimensions of the board after reading in
……..#WARNING: dimensions are 1 larger than largest index, since indices start at 0
……..self.maxRowMain = len(self.mainBoard)
……..self.maxColMain = len(self.mainBoard[0])

……..#Close the file
……..initialGenerationFile.close

….def displayBoard(self):
……..for rowIndex, row in enumerate(self.mainBoard):

…………for colIndex, col in enumerate(row):
…………….if self.mainBoard[rowIndex][colIndex]== “1”:
………………..print(“X”, end=”)
…………….else:
………………..print(“.”, end=”)

…………print() #print newline at end of each row

….def makeBoardCurrent(self): #TODO: Think of a better name — means to copy from the next-generation workingBoard to mainBoard
……..self.mainBoard = self.workingBoard
……..
….def calculateNextGeneration(self):
……..#Calculate next generation on workingBoard based on mainBoard

……..#Initialize work area
……..self.workingBoard = [] #A work area for creating the next Life generation

……..#Calculate next generation on workingBoard based on mainBoard
……..for mainRowIndex, mainRow in enumerate(self.mainBoard):

…………#Initialize working row before using for each row
…………workingRow = [] #for building up workingBoard row by row

…………for mainColIndex, mainElement in enumerate(mainRow):

…………….#Restart count of live cells
…………….numLiveCells = 0

…………….for i in [-1, 0, 1]:
………………..#Check row before, same row, next row
………………..rowOfCellToCheck = mainRowIndex + i

………………..#Wraparound
………………..if rowOfCellToCheck (self.maxRowMain – 1):
……………………rowOfCellToCheck = 0
……………………
………………..for j in [-1, 0, 1]:
……………………#Check column before, same column, next column
……………………colOfCellToCheck = mainColIndex + j

……………………#Wraparound
……………………if colOfCellToCheck (self.maxColMain – 1):
……………………….colOfCellToCheck = 0

……………………#If cell to check is alive, increment count of live cells
……………………#But if same row and column, ignore
……………………sameColAndRow = abs(i) + abs(j)
……………………if sameColAndRow != 0:
……………………….if self.mainBoard[rowOfCellToCheck][colOfCellToCheck] == “1”:
………………………. numLiveCells = numLiveCells + 1
…………………………………………

…………….if self.mainBoard[mainRowIndex][mainColIndex] == “1”: # The survival rules

………………..if 2 <= numLiveCells <= 3:
……………………workingRow.append(‘1’)
………………..else:
……………………workingRow.append(‘0’)

…………….else: #The reproduction rule

………………..if numLiveCells == 3:
……………………workingRow.append(‘1’)
………………..else:
……………………workingRow.append(‘0’)
……………………
…………self.workingBoard.append(workingRow)
…………………………..
#The actual main Life program
#Usage will be Life(filename, generations to calculate, every how many generations to display, display yes/no, write to files yes/no)
#First Usage Life() — done 22-Jul 10:24
#Second Usage Life(filename) — reading in file done 22-Jul-2015 10:59
#Third Usage Life(filename) — including displaying the file and dummy next generation 22-Jul-2015 18:34
#Fourth Usage Life(filename) — real next generation done 22-Jul-2015 20:17
#Fifth Usage Life(filename, generations to calculate, every how many generations to display) done 23-Jul-2015 20:44
#NOTE: Decided not to implement writing single generations to separate files. Seems unnecessary and would just fill my disk with lots of files.
#NOTE: Piping console output to text file is fine. Modern text editors can open large, multi-generation Life files and navigate quickly
#TODO: Next learning topics (backlog) would be:
#….1. Graphic display
#….2. Mouse input of boards
#….3. Change to argparse for robust command line parsing
#….4. Clean up file layout according to some accepted Python style guide
#….5. Refactor to be more functional as opposed to procedural, and reduce global variable use, if that makes code clearer

#Create a single Life instance
myLife = Life()

#Get the command line arguments
#TODO:Switch to Python argparse module instead

#From first command line argument, get pathname of initial (zero’th) generation text file
initialGenerationFilename = sys.argv[1]

#From second command line argument, get number of generations to calculate
numGenerations = int(sys.argv[2])

#From third command line argument, get period: every how many generations to display or write to file
#NOTE: currently, writing results to a file is not yet included
periodOfDisplay = int(sys.argv[3])

#Read in the initial (zero’th) generation board from text file
myLife.readBoardFromFile(initialGenerationFilename)

#Display initial (zero’th) generation
print(“Generation #”,0)
myLife.displayBoard()
print()

#Generate and display following generations
for generationIndex in range(1,numGenerations+1): #NOTE:Add 1 because range end is always one less than value
….myLife.calculateNextGeneration()
….myLife.makeBoardCurrent()
….if (generationIndex % periodOfDisplay) == 0: #NOTE: “%” is Python modulus — checking for evening divisible by period of display
……..print(“Generation #”,generationIndex)
……..myLife.displayBoard()
……..print()

And here’s some output. The 4-generation-period “glider” on a 25 x 25 grid, starts its flight from upper-left towards lower-right.
The command I ran was

Life.py Glider25by25.txt 8 4

and the output was

Generation # 0
..X......................
...X.....................
.XXX.....................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................

Generation # 4
.........................
...X.....................
....X....................
..XXX....................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................

Generation # 8
.........................
.........................
....X....................
.....X...................
...XXX...................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................
.........................

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Learning a New Programming Language, with Life (part 2)

I started learning Python two days ago, as described in part 1.

Yesterday I learned about Python Classes and Functions, including class and instance variables, and the special __init__ function. Today I learned enumerate, and the list function rstrip. I also learned not to forget the colon (:) in def, for, if, and else constructs!

After just a few hours today, my first project has actually started working.

For one “generation”, according to the rules of Conway’s Game of Life.

Here it is, complete with TEST comments preceding debugging code, and TODO comments for what’s next.

#Life.py

#Implementation of Conway's Game of Life
#See https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life

#Tom Harris 22-Jul-2015

#Import libraries needed
import sys #for command line argument support

#Global functions
def initialGenerationFilename():
….#Get pathname from first command line argument
….return sys.argv[1]

#Define the Life class

class Life:
….#class attributes
….#None

….#class methods

….def __init__(self):
……..#instance attributes: define and initialize (some more later after reading in file)
……..self.mainBoard = [] #The board of cells
……..self.workingBoard = [] #A work area for creating the next Life generation
….
….def readBoardFromFile(self, filename):
……..#Open the file
……..initialGenerationFile = open(filename)

……..#Read from the file, line by line:
……..for line in initialGenerationFile:
…………listLine = list(line.rstrip(‘\r\n’))
…………self.mainBoard.append(listLine) #add the line, in Python list format, to the mainBoard

……..#Determine dimensions of the board after reading in
……..#WARNING: dimensions are 1 larger than largest index, since indices start at 0
……..self.maxRowMain = len(self.mainBoard)
……..self.maxColMain = len(self.mainBoard[0])

……..#Close the file
……..initialGenerationFile.close

……..return self.mainBoard

….def displayBoard(self):
……..for rowIndex, row in enumerate(self.mainBoard):

…………for colIndex, col in enumerate(row):
…………….if self.mainBoard[rowIndex][colIndex]== “1”:
………………..print(“*”, end=”)
…………….else:
………………..print(“.”, end=”)

…………print() #print newline at end of each row

……..return 0 #TODO: replace with returning a result — what do we do with it? This is a function, not a procedure.

….def makeBoardCurrent(self): #TODO: Think of a better name — means to copy from the next-generation workingBoard to mainBoard
……..self.mainBoard = self.workingBoard
……..
……..return self.mainBoard

….def calculateNextGeneration(self):

……..#Calculate next generation on workingBoard based on mainBoard
……..workingRow = [] #for building up workingBoard row by row

……..#Calculate next generation on workingBoard based on mainBoard
……..for mainRowIndex, mainRow in enumerate(self.mainBoard):
…………for mainColIndex, mainElement in enumerate(mainRow):

…………….#Restart count of live cells
…………….numLiveCells = 0

…………….for i in [-1, 0, 1]:
………………..#Check row before, same row, next row
………………..rowOfCellToCheck = mainRowIndex + i

………………..#Wraparound
………………..if rowOfCellToCheck < 0:
……………………rowOfCellToCheck = self.maxRowMain – 1

………………..if rowOfCellToCheck > (self.maxRowMain – 1):
……………………rowOfCellToCheck = 0
……………………
………………..for j in [-1, 0, 1]:
……………………#Check column before, same column, next column
……………………colOfCellToCheck = mainColIndex + j

……………………#Wraparound
……………………if colOfCellToCheck < 0:
……………………….colOfCellToCheck = self.maxColMain – 1

……………………if colOfCellToCheck > (self.maxColMain -1):
……………………….colOfCellToCheck = 0

……………………#If cell to check is alive, increment count of live cells
……………………#But if same row and column, ignore
……………………sameColAndRow = abs(i) + abs(j)
……………………if sameColAndRow != 0:
……………………….if self.mainBoard[rowOfCellToCheck][colOfCellToCheck] == “1”:
………………………. numLiveCells = numLiveCells + 1
…………………………………………

…………….if self.mainBoard[mainRowIndex][mainColIndex] == “1”: # The survival rules

………………..if 2 <= numLiveCells <= 3:
……………………workingRow.append(‘1’)
………………..else:
……………………workingRow.append(‘0’)

…………….else: #The reproduction rule

………………..if numLiveCells == 3:
……………………workingRow.append(‘1’)
………………..else:
……………………workingRow.append(‘0’)
……………………
…………self.workingBoard.append(workingRow)
…………workingRow = []
………………..
……..return self.workingBoard

#The actual main Life program
#Usage will be Life(filename, generations to calculate, every how many generations to display, display yes/no, write to files yes/no)
#First Usage Life() — done 22-Jul 10:24
#Second Usage Life(filename) — reading in file done 22-Jul-2015 10:59
#Third Usage Life(filename) — including displaying the file and dummy next generation 22-Jul-2015 18:34
#Fourth Usage Life(filename) — real next generation done 22-Jul-2015 20:17
#TODO: Fifth Usage Life(filename, generations to calculate, every how many generations to display)

#Create a single Life instance
myLife = Life()

#Run the methods in the right order
myLife.readBoardFromFile(initialGenerationFilename())
myLife.displayBoard() #TEST: display the mainBoard before generating
print()
myLife.calculateNextGeneration()
myLife.makeBoardCurrent()
myLife.displayBoard()

And here’s the output. It’s the simplest oscillator — the “Blinker”, one generation, with wraparound:

........
*.......
*.......
*.......
........
........
........
........
........

........
........
**.....*
........
........
........
........
........
........

Learning a New Programming Language, with Life

For an upcoming course to help science students master the computer as a tool for their work, by learning to code, I need to learn Python. I reviewed discussions on Python 2 vs Python 3, and chose the latter.

To operate in a new language, I only need to learn and practice four things:

1. Input
2. Storage and Retrieval
3. Processing
4. Output

(Wish I could program functionally, and avoid #2. But Python isn’t designed for functional programming.)

My traditional project for learning a new language is to code Conway’s Game of Life.

After my first 2 hours in Python, with Python 3.4.3 installed, and Google for answering my questions, I’ve covered command line arguments (though still without argparse for user error handling), input from text file, output to console, line-by-line storage, and character-by-character retrieval from a Python list.

I’ve also imported one Python module (sys), and gotten used to code blocks via indentation.

Here’s my code so far. Wish me luck as I continue learning!

#ReadTextFromFileAndDisplay.py

#Import libraries needed
import sys #for command line argument support

#Get pathname of file to open from first command line argument
filenameToOpen = sys.argv[1]

#Open the file
myFile = open(filenameToOpen)
print("Pathname was: ", filenameToOpen)
print("Result code for opening the file was: \n", myFile)

#Read and display entire file
#Also store it in a list

myList = [] #declare list, initially empty

print("\nHere is the file as it's being read in: \n")
#Read from the file, line by line:
for line in myFile:
....print(line, end='') #display each line
....myList.append(line) #add the line to the list

#Close the file
myFile.close

print("\nFile should be closed now.\n")

print("Here's the contents of the list... \n")

#Display the contents of the list
for row in myList:
....print(row, end='') #entire rows
....print()
....for iCharacterIndex in range(len(row)):
........print(row[iCharacterIndex]) #character by character

p.s. I’ve put periods in to show the indentation, since it’s hard to get WordPress to preserve whitespace.