Session 4: Python File , Module, Class and Using Github

Session 4.1 Python Files and Class

1 The file system in Python

[Mission 4.1] The file path

First we need to know where is the file will be load and save to.

Bellow code will get the path current code is running.

import os
path = os.getcwd()
print(path)

[Mission 4.2] Saving and Loading file with Python

Write the string to the default path

myFile=open("Data.txt","w")
myFile.writelines("test string")
myFile.close()

the 2nd arguments of the open command is “w”, which is mean writing permission.

Mode	Description
‘r’	Open a file for reading. (default)
‘w’	Open a file for writing. Creates a new file if it does not exist or truncates the file if it exists.
‘x’	Open a file for exclusive creation. If the file already exists, the operation fails.
‘a’	Open for appending at the end of the file without truncating it. Creates a new file if it does not exist.
‘t’	Open in text mode. (default)
‘b’	Open in binary mode.
’+’	Open a file for updating (reading and writing)

Below example will show how to open a file given a file path, Also you \ is escape character, \\ make sure the program read the \, because \t mean add a tab, and \r is line break.

myFile1=open("C:\\Python\\Data.txt","w")
myFile1.writelines("test line1")
myFile1.writelines("\tcontinue on line1")
myFile1.writelines("\ntest line2")  # add a line break \n
myFile1.close()

myFile2=open("C:\\Python\\Data.txt","r")
print("line1:"+myFile2.readline()) #read first line
print("line2:"+myFile2.readline()) #it will auto ready next line

myFile2.close()

2 Dumping and Loading set of data to Files with `Pickle` Module

[Mission 4.3] Save a list to file with `Pickle`

Pickle is a module to help to hand save and load files, especially when you have a bunch of data need to save.

For using Pickle, you need use b model to save data in binary.

import pickle
list=[1,2,3,4,5]
myFile=open("testData.txt","wb")
pickle.dump(list,myFile)

import pickle

myFile=open("testData.txt","rb")
list= pickle.load(myFile)
print(list)

please run it and check the file.

[Mission 4.3] the different of `from import` and `import` the module

In the previous example we use import pickle, and when you use the pickle module, you need call with the module name. ex

import pickle
...
pickle.dump(list1,myFile)
...
list2=pickle.load(myFile)

if you only need use some function of the pickle, you could just from ... import to import the function you need. In this case, you will needn’t pass the module name.

from pickle import dump  # only dump be import
...
dump(list1,myFile)

also you could import all functions with wildcat *

from pickle import *
...
dump(list1,myFile)
...
list2=load(myFile)

Change your code and run to see the different.

[homework-1] [Mission 4.4] Refactor you code of you pixel arts

For your home work in the last session, please refactor the code, and save the list to file with pickle.
also the cube could be saved as as file name cube.txt too. hint you need one file to save your list to file with binary mode. Then modify your previous homework to read the data from the file and build structure in minecraft.

[homework-2] [Mission 4.5] Save a building structure to a list and dump to a file

Let’s see the below code example to read the current structure in your game, and save it as file.

from mcpi_e.minecraft import Minecraft
from mcpi_e import block

import pickle

serverAddress="192.168.1.155" # change to your minecraft server
playerName ="stoneskin2020"
pythonApiPort=4711

mc=Minecraft.create(serverAddress,pythonApiPort,playerName) 

#this function make sure the smaller number as value1
def sortPair(v1,v2):
    if v1>v2:
        return v2,v1
    else:
        return v1,v2

# this function will get the value of blockId in the input location and save as 3d list
def copyStructure(x1,y1,z1,x2,y2,z2):
    x1,x2 = sortPair(x1,x2)
    y1,y2 = sortPair(y1,y2)
    z1,z2 = sortPair(z1,z2)

    structure=[]
    print ("starting build the data structure...")
    for x in range(x1,x2):
        listX=[]
        structure.append(listX)
        for y in range(y1,y2):
            listY=[]
            listX.append(listY)
            for z in range(z1,z2):
                #print("x:{},y:{},z:{}".format(x,y,z))
                blockId=mc.getBlock(x,y,z)
                listY.append(blockId)
            print(listY)
    return structure

print("This python code will save the minecraft structure to the file")
input("Move to the first position, and press Enter:")
(x1,y1,z1)=pos1=mc.player.getTilePos()
input("Move to the second position, and press Enter:")
(x2,y2,z2)=pos2=mc.player.getTilePos()

data=copyStructure(x1,y1,z1,x2,y2,z2)
print(data)
filename=input("Please give a file name you want to save:")
if(filename==""):
    filename="test_tata"
filename=filename+".txt"
print("will save as "+filename)

theFile=open(filename,"wb")
pickle.dump(data,theFile)

[Home work] Please run the code save a structure as file, and write a code to load the file and rebuild the structure.

3 Object-oriented Basic

Object Oriented programming (OOP) is a method of structuring a program by bundling related properties and behaviors into individual objects.

Think about your code is a farm or factory, there is buildings, farmers, animals, workers ( builders, helpers etc). And your programming output is the products. All are objects and each objects will have it’s own properties, behaviors.

The Class is the template to create instance of objects. In python, it’s a module that could have a group of variable and functions.

OOP has four major principles, if want lear more please read this or how to explain object-oriented programming concepts to a 6 tear old

oop-concepts

[Mission 4.6] Create your first Class and Object

For learning python Class and Object, please read more.

The name convention of the Class is it’s name should start with Upper case

Define a class:

# this is a empty class
class Test():
    pass

Define a class “Cat”:

class Cat(object):
    def __init__(self,name,weight):
        self.name = name
        self.weight = weight

The Class has a special function __init__ it call contractor. it response to init the class. see below example of create a instance of the Cat class.

To make two new Cats object and add it to list

aKitten=Cat("kitty",2)
aCat = Cat("fluff",4)

# a instance could be added to list
cats=[]
cats.append(aKitten)
cats.append(aCat)

Note: you can’t use pickle to dump a class directly, you have to serialize it to string before save to file, read more if you interesting.

[Mission 4.7] Accessing Attributes of a class

You can access the attributes of an object.

theCat = Cat("theCat",4.5)
print("the Cat's name is '{}', and weight is {} ".format(theCat.name,theCat.weight))

[Mission 4.8] Add methods to Class

The Class could have multiple methods beside the constructor __init__

class Dog:
    species = "Canis familiaris"

    def __init__(self, name, age):
        self.name = name
        self.age = age

    # Instance method
    def description(self):
        return f"{self.name} is {self.age} years old"

    # Another instance method
    def speak(self, sound):
        return f"{self.name} says {sound}"

To use the methods defined in class

wang = Dog("a-wang",4)

print(wang.speak("woof woof"))

print(wang)

you will see if you print a instance of your class, it’s give result like

__main__.Dog object at 0x00aeff70>

There is special function to make it return the right format:

class Dog:
    # Leave other parts of Dog class as-is

    # Replace .description() with __str__()
    def __str__(self):
        return f"{self.name} is {self.age} years old"

please try it in your code.

** Object Oriented programming will continue in next session **