In-class notes for 04/11/2014

CS 121B (CS1), Spring 2014

• ______

Submitted questions on assignments and technology

Upcoming

• Homework 23

• Science Symposium

  • Three remaining events, all in Tomson 280

    • Friday 3:00pm speaker -- up to 2 point EC for a half-page response

    • Friday 4:30pm speaker -- up to 2 point EC for a half-page response

    • Friday 7:30pm CS speaker -- up to 4 points EC for a half-page response

    Please share a google doc with me, and start its title with   cs1S14 username  , e.g.,  cs1S14 rab .

Classes we have seen so far

• An object is a programming entity that has state variables (memory locations, to hold data) and methods (operations on the state variables)

• A class is a type of object.

  Objects in the same class have the same state-variable structure, and the same collection of methods.

• Return value from type() indicates the class of an object

• Classes we have seen that are built-in to Python3:

  • list. Example method: sort()

  • str. Many example methods, such as split(), strip(), and lower()

  • tuple. Example method: count(val)

  • dict. Example method: keys()

  • int, float, bool, and range are also implemented as classes in Python3, although we seldom call their methods

    (-4.0).isinteger() --> True

• Other classes we have seen that are not built-in, but are defined in standard Python3 modules:

  • turtle.Turtle. Many methods such as forward(), left(), pencolor()

  • turtle._Screen. Methods such as exitonclick()

• Classes we have seen that are not built-in and are not defined in standard Python3 modules:

  • cImage.Image. Methods such as draw(), setPixel(), getHeight()

  • cImage.ImageWin. Methods such as exitonclick()

• A programmer-defined class (not built-in, not defined in a standard module):

  • Account, defined by ~cs121/Account.py, spec in this link. Methods such as getBalance(), deposit()

Defining classes

• Memory diagram of an Account object

  Objects in the same class have the same state-variable structure, although each has its own separate memory locations.

• Syntax of a class definition

Exercise

• (Recall first and second animal dictionaries)

• Exercise 1:

  Define a Python3 class Animal that satisfies the following spec:

  • 3 state variables: name, species, fact
  • Constructor should have 3 args (plus self)
  • Methods: getName(), getSpecies, getFact(), setFact()

  Also, write code to accomplish the following:

  1. Construct two animal objects (e.g., lion and dog)
  2. Retrieve value of the name state variable for first object
  3. Retrieve value of the species state variable for second object
  4. Change the value of the fact state variable for second object, then retrieve the new value

Submitted questions on readings

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