Object-Oriented Programming#
Class#
Each class has its defined attributes and methods
# Define a class
class Employee:
# Constructor method
def __init__(self, first, last, pay):
self.first = first
self.last = last
self.email = first + '.' + last + '@email.com'
self.pay = pay
# instance method
def fullname(self):
return '{} {}'.format(self.first, self.last)
emp_1 = Employee('Corey', 'Schafer', 50000)
emp_2 = Employee('Test', 'Employee', 60000)
Types of Methods#
Class Method: a method bound to the class and with
cls
as the first default argumentStatic Method: a self-contained method bound to the class
Instance Method: a method bound to the object instance of the class with
self
as the first default argument
class Employee:
num_of_emps = 0
raise_amt = 1.04
def __init__(self, first, last, pay):
self.first = first
self.last = last
self.email = first + '.' + last + '@email.com'
self.pay = pay
Employee.num_of_emps += 1
def fullname(self):
return '{} {}'.format(self.first, self.last)
def apply_raise(self):
self.pay = int(self.pay * self.raise_amt)
@classmethod
def set_raise_amt(cls, amount):
cls.raise_amt = amount
@classmethod
def from_string(cls, emp_str):
first, last, pay = emp_str.split('-')
return cls(first, last, pay)
@staticmethod
def is_workday(day):
if day.weekday() == 5 or day.weekday() == 6:
return False
return True
emp_1 = Employee('Corey', 'Schafer', 50000)
emp_2 = Employee('Test', 'Employee', 60000)
Employee.set_raise_amt(1.05)
print(Employee.raise_amt)
print(emp_1.raise_amt)
print(emp_2.raise_amt)
emp_str_1 = 'John-Doe-70000'
emp_str_2 = 'Steve-Smith-30000'
emp_str_3 = 'Jane-Doe-90000'
first, last, pay = emp_str_1.split('-')
#new_emp_1 = Employee(first, last, pay)
new_emp_1 = Employee.from_string(emp_str_1)
print(new_emp_1.email)
print(new_emp_1.pay)
import datetime
my_date = datetime.date(2016, 7, 11)
print(Employee.is_workday(my_date))
1.05
1.05
1.05
John.Doe@email.com
70000
True
Class Inheritance#
The key of OOP
Extend the original class constructor methods using
super()
class Employee:
raise_amt = 1.04
def __init__(self, first, last, pay):
self.first = first
self.last = last
self.email = first + '.' + last + '@email.com'
self.pay = pay
def fullname(self):
return '{} {}'.format(self.first, self.last)
def apply_raise(self):
self.pay = int(self.pay * self.raise_amt)
class Developer(Employee):
raise_amt = 1.10
def __init__(self, first, last, pay, prog_lang):
super().__init__(first, last, pay)
self.prog_lang = prog_lang
class Manager(Employee):
def __init__(self, first, last, pay, employees=None):
super().__init__(first, last, pay)
if employees is None:
self.employees = []
else:
self.employees = employees
def add_emp(self, emp):
if emp not in self.employees:
self.employees.append(emp)
def remove_emp(self, emp):
if emp in self.employees:
self.employees.remove(emp)
def print_emps(self):
for emp in self.employees:
print('-->', emp.fullname())
dev_1 = Developer('Corey', 'Schafer', 50000, 'Python')
dev_2 = Developer('Test', 'Employee', 60000, 'Java')
mgr_1 = Manager('Sue', 'Smith', 90000, [dev_1])
print(mgr_1.email)
mgr_1.add_emp(dev_2)
mgr_1.remove_emp(dev_2)
mgr_1.print_emps()
Sue.Smith@email.com
--> Corey Schafer
Special Methods#
Dunder methods (double-underscore)
To avoid overloading the expressions in coding
class Employee:
raise_amt = 1.04
def __init__(self, first, last, pay):
self.first = first
self.last = last
self.email = first + '.' + last + '@email.com'
self.pay = pay
def fullname(self):
return '{} {}'.format(self.first, self.last)
def apply_raise(self):
self.pay = int(self.pay * self.raise_amt)
def __repr__(self):
return "Employee('{}', '{}', {})".format(self.first, self.last, self.pay)
def __str__(self):
return '{} - {}'.format(self.fullname(), self.email)
def __add__(self, other):
return self.pay + other.pay
def __len__(self):
return len(self.fullname())
emp_1 = Employee('Corey', 'Schafer', 50000)
emp_2 = Employee('Test', 'Employee', 60000)
# print(emp_1 + emp_2)
print(len(emp_1))
13
Property Decorator#
@property
: make a method function like attribute-accessing@NAME.setter
: make a method function like class-attribute assigning@NAME.deleter
: make a method function like class-attribute deleting
class Employee:
def __init__(self, first, last):
self.first = first
self.last = last
@property
def email(self):
return '{}.{}@email.com'.format(self.first, self.last)
@property
def fullname(self):
return '{} {}'.format(self.first, self.last)
@fullname.setter
def fullname(self, name):
first, last = name.split(' ')
self.first = first
self.last = last
@fullname.deleter
def fullname(self):
print('Delete Name!')
self.first = None
self.last = None
emp_1 = Employee('John', 'Smith')
emp_1.fullname = "Corey Schafer"
print(emp_1.first)
print(emp_1.email)
print(emp_1.fullname)
del emp_1.fullname
Checking Functions#
isinstance()
: Check an instance’s typeissubclass()
: Check class inheritance
Name Mangling#
__NAME
: Any identifier of this form within the class is textually replaced with_classname__NAME
, whereclassname
is the current class name, with leading underscore(s) stripped.This is for the purpose of creating private variables to the class.
Reference#
This notebook is based on Corey Schafer’s OOP Tutorial