[course]07 —— 面向对象编程 01

1. Methods vs Functions

We call methods using s.f() rather than f(s):

s = 'This could be any string!'

print(len(s))     # len is a function

print(s.upper())  # upper is a string method, called using the . notation
                  # we say that we "call the method len on the string s"

print(s.replace('could', 'may')) # some methods take additional arguments

See how we get different errors for improperly calling methods vs functions:

n = 123
print(len(n))    # TypeError: object of type 'int' has no len()
                 # This means that len() cannot work properly with int's

n = 123
print(n.upper()) # AttributeError: 'int' object has no attribute 'upper'
                 # This means that there is no method upper() for int's

2. Classes and Instances

• Classes are also called "Types" in Python.

  • For example, these are classes: int, float, str, bool

• Instances are values of a given class or type.

  • For example: 'abc' is a str instance (also called a string)

3. Objects and Object-Oriented Programming (OOP)

• Every value in Python is an Object.

  • Every instance is an object, and its type is some class.

  • Every class is an object, too (its type is type!).

• That is why we call this Object-Oriented Programming

  • We are using objects only a little bit now.

  • Soon we will write our own classes.

  • Then we will add some sophistication to how we write and use classes and objects.

  • Even so, because we are using objects now, we are already using Object-Oriented Programming (OOP).