This Python __init__ Method lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
__init__ runs when the object is created. Use it to store the starting attributes. It does not return the new object. Python does that.
Arguments after self come from the call. Batch(\"Python\", 24) passes those two values.
Example 1: Start here
Forgetting self on an attribute creates a local variable that disappears when __init__ ends.
class Batch: # a template for objects
def __init__(self, topic, seats): # runs when you create the object
self.topic = topic # store this on the object
self.seats = seats # store this on the object
print(Batch("SQL", 20).seats)
Example 2: Required setup
__init__ runs automatically when you call the class.
class Course: # a template for objects
def __init__(self, title, seats): # runs when you create the object
self.title = title # store this on the object
self.seats = seats # store this on the object
print(Course("Python", 24).seats)
Example 3: A default in init
A default lets the caller omit seats.
class Course: # a template for objects
def __init__(self, title, seats=20): # runs when you create the object
self.title = title # store this on the object
self.seats = seats # store this on the object
print(Course("Python").seats)
Example 4: Validate in init
Fix bad values before they are stored on the object.
class Course: # a template for objects
def __init__(self, seats): # runs when you create the object
if seats < 0: # run the indented lines only when this is true
seats = 0 # a whole number
self.seats = seats # store this on the object
print(Course(-3).seats)
Forgetting self on an attribute creates a local variable that disappears when __init__ ends.
