This Python Inner Classes lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
A class written inside another class is an inner class. It fits a small type that only makes sense together with the outer one.
Build the inner object from the outer __init__ when each course should own its batch. The inner class does not automatically see the outer object.
Example 1: Start here
Pass the outer values the inner class needs. It does not receive them on its own.
class Course: # a template for objects
def __init__(self, topic): # runs when you create the object
self.topic = topic # store this on the object
self.batch = self.Batch(1) # store this on the object
class Batch: # a template for objects
def __init__(self, number): # runs when you create the object
self.number = number # store this on the object
def label(self): # define the function; it runs when you call it
return "Batch " + str(self.number) # send this value back to the caller
print(Course("Python").batch.label())
Example 2: A class inside a class
The inner class is reached through the outer class name.
class Course: # a template for objects
class Schedule: # a template for objects
def __init__(self, hour): # runs when you create the object
self.hour = hour # store this on the object
print(Course.Schedule(10).hour)
Example 3: Build it from a method
A method can return an instance of the inner class.
class Course: # a template for objects
class Schedule: # a template for objects
def __init__(self, hour): # runs when you create the object
self.hour = hour # store this on the object
def at(self, hour): # define the function; it runs when you call it
return self.Schedule(hour) # send this value back to the caller
print(Course().at(10).hour)
Example 4: A function is often enough
Use an inner class when the inner object has several methods. A dictionary is enough for one value.
def schedule(hour): # define the function; it runs when you call it
return {"hour": hour} # send this value back to the caller
print(schedule(10)["hour"])
Pass the outer values the inner class needs. It does not receive them on its own.
