CS52 - Fall 2015 - Class 12

Example code in this lecture

   while.py
   bit.py

Lecture notes

  • admin
       - how did assignment 4 go?
       - assignment 5
          - out
          - should be able to finish it after today's class

  • high level
       - look at first two functions of while.py code
       
       - lists

       - defining classes in python: look at bit.py code

  • python basics
       - running python and interacting with the python shell
          - python is an interpreted language, like SML
          - can just type "python" at the terminal to get a shell
          - execfile
             - like "use" in SML
             - it's a function, though:

                >>> execfile("while.py")
          

       - :
          - defines a block, we'll see it a lot
          - indentation indicates blocks (the role previously reserved for curly braces)
             - indentation is critical and is not just stylistically important

       - basic control flow
          - if/elif/else
          - for
             - use of range
          - while

       - defining functions
          - def
          - no return type
          - no parameter types
       
       - comments

       - docstrings

       - print
          - using str()

       - talk about pass

  • lists
       - similar to arrays in Java
          - indexable
          - can iterate over

       - some differences
          - actually a class, so they have methods
          - they're extensible and mutatable (sort of like ArrayList class in Java)
             - can append to them
             - can insert into them
             - can delete elements in them
       
       - creating with []
          >>> l = [1, 2, 3]
          >>> l
          [1, 2, 3]
          >>> l = ["apples", "bananas", "carrots"]
          >>> l
          ['apples', 'bananas', 'carrots']
          >>> l = [1, "apples", [1, 2]]
          >>> l
          [1, 'apples', [1, 2]]
       
       - indexing
          >>> l = [1, 2, 3, 4]
          >>> l2 = ["apples", "bananas", "carrots"]
          >>> l3 = [1, "apples", [1, 2]]

          - starts counting at 0, like in Java

          >>> l[0]
          1
          >>> l2[2]
          'carrots'
          >>> l3[1]
          'apples'

          - can index from the back using negative numbers

          >>> l[-1]
          4   

       - slicing
          - can also "slice" the list to get a sublist

          >>> l[1:3]
          [2, 3]


       - many methods (see the documentation)
          - append
             >>> l = []
             >>> l.append(2)
             >>> l.append(3)
             >>> l
             [2, 3]
          - indexing

       - iterating over
          - using for
          - talk about what range does


  • defining classes in python: look at bit.py code
    •