📝Week 9 - Lab Intro

In this lab introduction we will briefly review and discuss classes. We will also go over some of the math involved in triangulation, which will be useful for this week’s lab.

Classes

Creating a class

You can use the keyword class to create a class.

class MyClass:
    # contents of the class go indented here
    ...

Classes can contain various attributes, including variables and functions.

class MyClass:
    
    myVar = 9

    def myFunc():
        print("Hello World")

We can access these by doing the following:

MyClass.myFunc()
MyClass.myVar

Creating objects from classes

You can create objects belonging to a class. First, we must discuss the __init__ method.

The __init__ method

The __init__ method is a function that is used to handle the creation of new objects. The first input argument self is used to refer to the object being created. We can use self.<variable name> to create a variable specific to each object.

class Student:

    # the first input argument to init refers to the object being created
    # by convention it is always called "self"
    def __init__(self, fname, lname):
        # self.fname is a variable 
        self.fname = fname
        # self.lname is a variable 
        self.lname = lname

To create a new object of class Student, we can do the following.

# The two strings are passed as the second and third input arguments to the __init__ method
s1 = Student("John", "Foo")

We can create a different object belonging to the same class

s2 = Student("Jane", "Bar")

Each Student object has its own first and last name variables.

print(s1.fname)
print(s1.lname)

print(s2.fname)
print(s2.lname)

Adding methods

A method is defined just like a function where the first argument is self, referring to the current object. (Just like with __init__, the first argument of all methods is called self by convention.)

Below we define a method called print_full_name which prints the student’s full name.

class Student:

    def __init__(self, fname, lname):
        self.fname = fname
        self.lname = lname

    def print_full_name(self):
        print(f"{self.fname} {self.lname}")

When calling a method, the object itself is always passed in as the first argument. This is why there is nothing in the parentheses of the method calls below.

s1 = Student("John", "Foo")
s2 = Student("Jane", "Bar")

s1.print_full_name()
s2.print_full_name()

Triangulation

We will now discuss the introduction to today’s lab.