Class anatomy: the __init__ constructor
Introduction to Object-Oriented Programming in Python
George Boorman
Curriculum Manager, DataCamp
Methods and attributes
- Methods are function definitions within a class
selfas the first argument- Define attributes by assignment
- Refer to attributes in class via
self.___ - Calling lots of methods could become unsustainable!
class MyClass: # function definition in class # first argument is self def my_method1(self, other_args...): # do things heredef my_method2(self, my_attr): # attribute created by assignment self.my_attr = my_attr ...
Constructor
- Add data to object when creating it
- Constructor
__init__()method is called every time an object is created- Called automatically because of
__methodname__syntax
- Called automatically because of
class Customer:
def __init__(self, name):
# Create the .name attribute and set it to name parameter
self.name = name
print("The __init__ method was called")
Constructor
# __init__ is implicitly called
cust = Customer("Lara de Silva")
print(cust.name)
The __init__ method was called
Lara de Silva
Attributes in methods
class MyClass: def my_method1(self, attr1): self.attr1 = attr1 ... def my_method2(self, attr2): self.attr2 = attr2 ...obj = MyClass() # attr1 created obj.my_method1(val1) # attr2 created obj.my_method2(val2)
Attributes in the constructor
class MyClass: def __init__(self, attr1, attr2): self.attr1 = attr1 self.attr2 = attr2 ...# All attributes are created obj = MyClass(val1, val2)
- Generally we should use the constructor
- Attributes are created when the object is created
- More usable and maintainable code
Add arguments
class Customer: # Add balance argument def __init__(self, name, balance):self.name = name # Add the balance attribute self.balance = balance print("The __init__ method was called")
Add parameters
# __init__ is called
cust = Customer("Lara de Silva", 1000)
print(cust.name)
print(cust.balance)
The __init__ method was called
Lara de Silva
1000
Default arguments
class Customer:
# Set a default value for balance
def __init__(self, name, balance=0):
self.name = name
# Assign the new attribute
self.balance = balance
print("The __init__ method was called")
Default arguments
# Don't specify the balance explicitly cust = Customer("Lara de Silva")print(cust.name) # The balance attribute is created anyway print(cust.balance)
The __init__ method was called
Lara de Silva
0
Best practices
1. Initialize attributes in __init__()
Best practices
1. Initialize attributes in __init__()
2. Naming
CamelCase for classes, lower_snake_case for functions and attributes
Best practices
1. Initialize attributes in __init__()
2. Naming
CamelCase for class, lower_snake_case for functions and attributes
3. Keep self as self
class MyClass:
# This works but isn't recommended
def my_method(george, attr):
george.attr = attr
Best practices
1. Initialize attributes in __init__()
2. Naming
CamelCase for class, lower_snake_case for functions and attributes
3. self is self
4. Use docstrings
class MyClass:
"""This class does nothing"""
pass
Let's practice!
Introduction to Object-Oriented Programming in Python
