Getting Started with Python

1. Getting Started with Python Part I of Minecraft: Pi Edition October 17, 2015

2. Outlines • What is Python? • How to run a Python program? • Control constructs • Using language resources • Designing your program • Having fun with graphics • Setting up for Minecraft mod programming

3. What is Python? • High level programming language • Easy to use • Run from the Bang (aka Shell or console) or a file • A scripting language • Loosely typed • Write once and run on all supporting platforms • Freely available

4. A brief history of Python • First created by Guido von Rossum in late 1989 • named after the Brit-com Monty Python's Flying Circus • Python 2.0 was released on 16 October 2000, with many major new features including • a full garbage collector, and • support for unicode • Python 3.0 was released on 3 December 2008 • backwards-incompatible (to version 2.5 released in 2006) • Some features were backported to versions 2.6 (‘08) & 2.7 (‘10) • Latest version is 3.4

5. How Python is used? • Python is a general purpose programming language • Can be used on any modern computer operating system • Used for processing text, numbers, images, scientific data, and much more • It is used daily in the operations like • Googlesearch engine • the video sharing web site YouTube • NASA, and • the New York Stock Exchange

6. Setting in our labs • The Python shell (the Bang or console or command line) • Run your code directly • IDLE (Integrated DeveLopment Environment), which provides • Multi-window text editor • Python shell • Integrated debugger

7. Python Shell: easy to learn and use… • Arithmetic operations • 123*456 • Print text strings • print('Hi, There!') • Using a variable • prod=123*456 • print(prod) • A few more runs • print('Going…') • print('Going…') • print('Going…') • print('Gone!')

8. IDLE: put code in a file • Create a new file using File | New Window • Save the file with a .pyextension File | Save (As) • Create directory as needed • File name conventions • Run your program using Run | Run Module • print('Going…') • print('Going…') • print('Going…') • print('Gone!') • Write a comment line (starting with a #) • to be read by the programmers • not to be interpreted by machine

9. Control construct: using a for loop • Sometimes an operation needs to be repeated many times • Going, going, going … • Using a loop construct can save you some typing (and your code elegant) • Try out this for loop for x in range(1,4): print('Going…') • What does range(1, 4) generate? • Try outlist(range(1, 4))

10. Control construct: using if statement • In the for loop • If it’s one of the first 3 iterations:print('Going…') • Else, i.e., it’s the last and 4th time:print('Gone!')

11. Using resources: dealing with strings • A string object encloses a sequence of characters • To assign a string value to a variable, usebook_name = 'Programming the Raspberry Pi' • Try the following with Python shellbook_name 'Programming the Raspberry Pi' print(book_name) Programming the Raspberry Pi • How to get a part of a string? Try the following:book_name[1]  'r' book_name[0]  ‘P' book_name[0:11]  ‘Programming ' book_name[12:] 'the Raspberry Pi'

12. Using resources: dealing with strings • String concatenation: just use the + operatorbook_name + ' by Simon Monk' 'Programming the Raspberry Pi by Simon Monk' • The len()method • A method is a “function” that a class provides to do something • The method is provided by the String class[look up it at http://www.tutorialspoint.com/python/string_len.htm] • len(book_name)  28 • Other methods: try them out on your ownupper()lower()capitalize()

13. Using resources: importing a module • Features defined in one Python file is organized as a module • Many modules need to be imported before its features can be used: the random module • Generating a random number using:import randomdice_value = random.randint(1, 6) • Printing a number of dice values:import randomfor x in range(1, 10):dice_value = random.randint(1, 6) print(dice_value)

14. Using resources: The datetime module • Example: retrieve today’s date and print date/time parts import datetime # Get a date object today = datetime.date.today() # General functions print "Year: %d" % today.year print "Month: %d" % today.month print "Day: %d" % today.day print "Weekday: %d" % today.weekday() # Day of week Monday = 0, Sunday = 6 # ISO Functions print "ISO Weekday: %d" % today.isoweekday() # Day of week Monday = 1, Sunday = 7 print "ISO Format: %s" % today.isoformat() # YYYY-MM-DD format print "ISO Calendar: %s" % str(today.isocalendar()) # Tuple of (ISO year, ISO week number, ISO weekday) # Formatted date print today.strftime("%Y/%m/%d") #

15. Using resources: a list of values • One variable (like dice_value) can only hold one value • If we want to store all the random values, a list can help Declare, initialize, & print dice_values 6 dice_values[0] dice_values = [2,3,1] print (dice_values) 4 Use one name to refer to all values in list dice_values[1] 3 dice_values[2] Create an empty list and append 3 dice_values = [] for x in range(1, 10): dice_values += _ [random.randint(1, 6)] dice_values[3] 2 dice_values[4] 6 dice_values[5] . . . . . . Use indexes (0-based) to refer to individual values Print one value in a line for x in range(1, len(dice_values)): print(dice_values[x])

16. Structured design: writing a function • When your program grows bigger, you may break it down to units known as functions • A function can be called repeatedly to do the same thing again and again • Some functions can return a value that other parts of your program can use Use the keyword def keep the indentation call the function

17. Structured design: code w/ a function • Executable code in the box below: import random dice_values = [] for x in range(1, 10): dice_values += [random.randint(1, 6)] defcompare_dice_value(your_value, my_value): return_str = 'Tie' if your_value > my_value: return_str = 'You win' if your_value < my_value: return_str = 'I win' returnreturn_str print compare_dice_value(dice_values[0], dice_values[len(dice_values)-1]) print compare_dice_value(dice_values[0], dice_values[0])

18. Object-orientation: object and class • When you program (or system) grows even BIGGER, OO design will be helpful • OO is about objects, i.e., software entities that combine data and operations on the data in one place • We have used objects in our examples (Python is an OO language after all), such as strings. >>> 'lower'.upper() 'LOWER' An objects belongs to a class, which can be found out using… >>> 'lower'.__class__ <type 'str'> >>> [1].__class__ <type 'list'> >>> 12.34.__class__ <type 'float'> Invoking the upper() method of the str class All values are objects, even a number!

19. Object-orientation: defining a class • In addition to using other people’s classes, you may make some of your own! • Here is one:ScaleConverter Use the keyword class Keep indentation for body of the class Create an object of a certain type Keep indentation for body of each method Call a method Use a variable

20. Object-orientation: the ScaleConverterclass • Executable code in the box below: #05_01_converter classScaleConverter: def__init__(self, units_from, units_to, factor): self.units_from = units_from self.units_to = units_to self.factor = factor def description(self): return 'Convert ' + self.units_from + ' to ' + self.units_to def convert(self, value): return value * self.factor c1 = ScaleConverter('inches', 'mm', 25) print(c1.description()) print('converting 2 inches') print(str(c1.convert(2)) + c1.units_to) data operations

21. Object-orientation: inheritance by subclassing • Observations tell us objects in real world come in types, and the types are related: such as types and subtypes • Design can be made easy if we subclass some class and the subclass can inherit features from the old super class • Let’s see how to make a ScaleAndOffsetConverter to extend the ScaleConverter so that we can convert temp. Link the two classes Override a method in the super class Method inherited from super class

22. O-O: the ScaleAndOffsetConverterclass • Executable code in the box below: class ScaleConverter: #implementation details omitted classScaleAndOffsetConverter(ScaleConverter): def __init__(self, units_from, units_to, factor, offset): ScaleConverter.__init__(self, units_from, units_to, factor) self.offset = offset def convert(self, value): return value * self.factor + self.offset c1 = ScaleConverter('inches', 'mm', 25) #… … c2 = ScaleAndOffsetConverter('C', 'F', 1.8, 32) print(c2.description()) print('converting 20C') print(str(c2.convert(20)) + c2.units_to)

23. GUI Programming: the tkinter module • Tkinter is the Python interface to the Tk GUI system • Tk is written in Tcl (tool command language) and is available for many platforms • Tkinter is only available for Python 3.x • From IDLE • From Python shell

24. GUI Programming: a Temp. Converter • A more sophisticate GUI with • A title in the title bar • A text field with a caption (label) to take input value: temp. in oC • A label with a caption (label) to display output value: temp. in oF • A “Convert” button to trigger the conversion • The ScaleAndOffsetConverterclass is used to do the calculation • The two converter classes (super- and sub-classes) are stored in a converters.py file • It is known as the converters module in the code as shown on the next slide • Code listed on the next slide

25. from tkinter import * from converters import * class App: def __init__(self, master): self.t_conv = ScaleAndOffsetConverter('C', 'F', 1.8, 32) frame = Frame(master) frame.pack() Label(frame, text='deg C').grid(row=0, column=0) self.c_var = DoubleVar() Entry(frame, textvariable=self.c_var).grid(row=0, column=1) Label(frame, text='deg F').grid(row=1, column=0) self.result_var = DoubleVar() Label(frame, textvariable=self.result_var).grid(row=1, column=1) button = Button(frame, text='Convert', command=self.convert) button.grid(row=2, columnspan=2) def convert(self): c = self.c_var.get() self.result_var.set(self.t_conv.convert(c)) root = Tk() root.wm_title('Temp Converter') app = App(root) root.mainloop()

26. GUI Programming: try it out yourself • How to change the interface to another style? • With deg C and deg F after the in- and output values • How to change the app into a converter from Fahrenheit to Celsius?

27. GUI Programming: try out the canvas • There are all kinds of widgets in the tkinter module • Here is a simple demo for how to use the canvas: from tkinter import * class App: def __init__(self, master): canvas = Canvas(master, width=400, height=200) canvas.pack() canvas.create_rectangle(20, 20, 180, 180, fill='white') canvas.create_oval(90, 90, 110, 110, fill='#ff2277') canvas.create_rectangle(220, 20, 380, 180, fill='white') canvas.create_oval(290, 90, 310, 110, fill='#ff2277') root = Tk() app = App(root) root.mainloop() DIY Project: Try to use random and define some class(es) to display all possible dice throws. Add a button to roll the dices again and again.

28. Setting up the Raspberry Pi • Open a web browser on Raspberry Pi • Visit http://pi.minecraft.net • Go to the Download page • Download the latest version of the game • Save the file in the /home/pi directory • Open a fresh terminal and enter thefollowing command: • tar –zxvfminecraft-pi-<version>.tar.gz • Change directory with cd mcpi • ./minecraft-pi • a new window should pop up with Minecraft: Pi Edition running inside

29. What’s Next? • Programming Python on the Pi • A “Hello, Minecraft!” demo • 2D list (or array), how to use it? • Using Minecraft modules • Coding and testing a 2D board game • Putting the board game into Minecraft To be continued next Friday, October 24.