This Python Polymorphism lesson is for a beginner. Read the short notes, run each example, then change one name or number and run it again.
Polymorphism means different objects can answer the same method name. A loop can call label() without asking which class each object is.
Python does not require a shared parent for this. If the method exists, the call works.
Example 1: Start here
Keep the shared method name and the meaning aligned. Two label methods should both return a label.
class Pdf: # a template for objects
def label(self): # define the function; it runs when you call it
return "PDF" # send this value back to the caller
class Sheet: # a template for objects
def label(self): # define the function; it runs when you call it
return "Sheet" # send this value back to the caller
for item in (Pdf(), Sheet()): # repeat the indented lines once per value
print(item.label())
Example 2: Same call, different classes
The loop does not care which class it has, as long as label exists.
class PythonCourse: # a template for objects
def label(self): # define the function; it runs when you call it
return "Python" # send this value back to the caller
class SqlCourse: # a template for objects
def label(self): # define the function; it runs when you call it
return "SQL" # send this value back to the caller
for course in (PythonCourse(), SqlCourse()): # repeat the indented lines once per value
print(course.label())
Example 3: A shared parent
The child supplies its own label. Callers can still treat it as a Course.
class Course: # a template for objects
def label(self): # define the function; it runs when you call it
return "Course" # send this value back to the caller
class PythonCourse(Course): # a template for objects
def label(self): # define the function; it runs when you call it
return "Python" # send this value back to the caller
print(PythonCourse().label())
Example 4: Duck typing
Python uses the methods an object has. The classes do not need a shared parent.
class Batch: # a template for objects
def size(self): # define the function; it runs when you call it
return 24 # send this value back to the caller
class Waitlist: # a template for objects
def size(self): # define the function; it runs when you call it
return 5 # send this value back to the caller
def show(group): # define the function; it runs when you call it
print(group.size())
show(Batch()) # call the function
show(Waitlist()) # call the function
Keep the shared method name and the meaning aligned. Two label methods should both return a label.
