Index

1. Lecture: 2-1

• Prerequisites for this lecture are: 1-1 and .

2. Python

• Python is a scripting language

3. Python Gotha’s

• blocks are defined by indentation!
• turn off tabs in your favourite editor
• in your own programs examples never create a name clash with a Python library module
• Python2 vs Python3
  • we will be using Python3

4. Python verses similar tools

• Python is a scripting language
  • it can be compiled if necessary to increase speed
• is more powerful than many other scripting languages, Tcl
  • applicable to larger systems development (games, net admin)
• has a much cleaner syntax than Perl
  • easier to maintain
• does not compete head on with Java
  • Java is a systems language like C++

5. Python and games

• examples of games which use Python

6. Python can be simple

• #!/usr/bin/python3
  
  print("hello world")

7. Python Modules allow for problem decomposition

• similar to Modula-2

• myfile.py

  #!/usr/bin/python3
  
  title = "hello world"

• 
  foo.py

  #!/usr/bin/python3
  
  import myfile
  print(myfile.title)

• when run prints hello world
  

8. Alternative import

• bar.py

  #!/usr/bin/python3
  
  from myfile import title
  print(title)

• note that all python modules need to be saved as name.py
  • so in our example the module myfile was saved into a file called myfile.py
    

9. Python builtin types

• python contains many builtin types
  • use them..
• builtin objects make simple programs easy to understand
  • lists, dictionaries, exist, don’t reinvent the wheel
• built in objects are more efficient than custom data types

10. Builtin objects

11. Expression operators

12. Strings

• concatenation via +
  • repeated via *

• #!/usr/bin/python3
  
  print("hi " * 4)

• yields

• hi hi hi hi

13. Slicing

• given a string, s= "hello world"
  • can obtain portion of string via: s[2:5]
  • yields: llo
• first character has index 0
  • and also -11
  • last character index is 10 in this example
  • last character index is also -1
• negative values start at right and move to the left
• strings can be sliced using positive and negative values

14. Using dir

• often you may wish to see what methods a module provides
  • run python interactively

• python
  Python 1.5.2
  >>> import string
  >>> dir(string)
  [’capitalize’, ’capwords’, ’center’, ’count’, \
   ’digits’, ’expandtabs’, ’find’, ’hexdigits’, \
   ’index’, ’index_error’, ’join’, ’joinfields’, \
   ’letters’, ’ljust’, ’lower’, ’lowercase’, \
   ’lstrip’, ’maketrans’, ’octdigits’, ’replace’, \
   ’rfind’, ’rindex’, ’rjust’, ’rstrip’, ’split’, \
   ’splitfields’, ’strip’, ’swapcase’, \
   ’upper’, ’uppercase’, ’whitespace’, ’zfill’]

• displays methods available
  

15. Methods and documentation

• python online docs
  • under GNU/Linux
• tutorial/laboratory
  • read through the online tutorial under the web address above
  • read about functions and scope rules
    • name resolution, LGB rule
    • local, global, builtin scope

16. Statements

• assignment, calls, if/else/elif, for, while, break/continue
  • print used to be a statement in Python 2, it is a function in Python 3
• try, except, raise,
• def, return
  • function definitions and returning values

17. Statements

• class
• assert
• exec
• del
• global

18. Example 8 times table

• #!/usr/bin/python3
  
  
  for n in range(1, 13):
      print(n, "x 8 =", n*8)

• $ python3 eight.py
  1 x 8 = 8
  2 x 8 = 16
  3 x 8 = 24
  4 x 8 = 32
  5 x 8 = 40
  6 x 8 = 48
  7 x 8 = 56
  8 x 8 = 64
  9 x 8 = 72
  10 x 8 = 80
  11 x 8 = 88
  12 x 8 = 96

19. Example of for loop

• #!/usr/bin/python3
  
  
  
  for n in range(2, 10):
      print("n is", n)
  else:
      print("finished for loop, n is", n)

• ./py7.py
  n is 2
  n is 3
  n is 4
  n is 5
  n is 6
  n is 7
  n is 8
  n is 9
  finished for loop, n is 9

20. Tricky example code

• #!/usr/bin/python3
  
  
  for n in range(2, 10):
      print("n is", n)
      for x in range (2, n):
          print("x is", x)
          if n % x == 0:
              print(n, "equals", x, "*", n/x)
              break
      else:
          print(n, "is a prime number")

• ./py6.py
  2 is a prime number
  3 is a prime number
  4 equals 2 * 2
  5 is a prime number
  6 equals 2 * 3
  7 is a prime number
  8 equals 2 * 4
  9 equals 3 * 3

21. Install tkinter for Python

• in your GNU/Linux installation start a terminal and type:

• $ sudo apt install python3-tk

• answer Y to all the questions, this will install tkinter for Python3 permanently on your system
  

22. Graphical hello world as an example of Python simplicity

• #!/usr/bin/python3
  
  import tkinter
  
  def makebutton (message):
          w = tkinter.Button (text=message, command="exit")
          w.pack ()
          w.mainloop ()
  
  makebutton ("Hello world")

Index

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