1. CSE 231 Lab 11

2. Topics to Cover Today Classes Creating classes
Attributes and Methods in class
Instantiate class

3. Classes
You’ve been working with a bunch of different classes all semester: list, set, dict, etc.
A class outlines how to “make” something and what that something “is.”
Classes are an Object Oriented Programming (OOP) paradigm.

4. Classes

5. Class and Instance D = set({1,2,3,4})
Creates an instance from set class
set() is the constructor of the class set
Class is like a cookie cutter
Instance is like a cookie

6. Classes – Creating a Class
# here is the bare minimum you need to make a class in Python class ClassName(): pass

7. What is the purpose of this method?
def __init__(self, A = 0, B = 1):
self.__a = A
self.__b = B
The moment you ask for an instance of a class to be created, the __init__ function is called.
So if you need to setup anything for an object,
it should go in init.

8. Classes – What is __init__?
Arguments you define for __init__ (besides self) are what you pass when you create an object. class SomeClass(): def __init__(self, name): self.name = name # instances have a member called name print(“HI ”, self.name)
>>> x = SomeClass()
# ERROR
Traceback (most recent call last): File "<stdin>", line 1, in <module>TypeError: __init__() missing 1 required positional argument: 'name'

9. Classes – What is __init__?
class SomeClass(): def __init__(self, name): self.name = name print(“Hi”, self.name) >>> x = SomeClass(‘Bob’) # good Hi Bob

10. Classes – What is __init__?
class SomeClass(): def __init__(self, name = ‘Bob’ ): self.name = name print(“Hi”, self.name)
>>> x = SomeClass()
# good
>>> x = SomeClass(‘ZACH’)
# good
Hi Bob
Hi ZACH

11. What happens? class Time:
def __init__(self, hour = 0, minute = 0, second = 0):
print(hour,minute,second)
What are the values of hour, minute and second if I create:
C = Time(50,7)
50 7 0
C = Time(second = 83, hour = 24))

12. What is the purpose of this method?
def __str__ (self):
out_str = “{},{}”.format(self._a,self._b)
return out_str

13. Classes – Making a Method
class SomeClass(): def __init__(self, number): self.number = number # member variable/attribute def get_square_number(self): return self.number ** 2
>>> x = SomeClass(2)
>>> x. get_square_number() 4

14. Classes – What is self?
class SomeClass(): def __init__(self, number): self.number = number def square(self): print(self.number**2) # <- self gets replaced with John!
>>> John = SomeClass(5)
>>> John. square() 25
>>> Bob = SomeClass(6)
>>> Bob. square() 36

15. Classes – What is self? NameError
class SomeClass(): def __init__(self, number): self.number = number def print_number(self): print(number)
>>> Bob = SomeClass(6)
>>> Bob.print_number()
NameError
# you forgot to mention self

16. Classes – What is self?
class SomeClass(): def __init__(self, number): self.number = number def print_number(self): print(self.number)
>>> Bob = SomeClass(6)
>>> Bob.print_number() 6