MediumExperience level: 3-5 years · 8-15 years1 min read

What is polymorphism and duck typing in Python?

Reviewed by Gurusankar M.

Asked inAmazonMicrosoftDeloitte
#polymorphism#duck typing#oop#protocol#interface
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Short Answer

Polymorphism means the same operation works on different types — the right method is chosen by the object. Python does this via duck typing: 'if it walks like a duck and quacks like a duck, it's a duck.' Code depends on behavior (methods an object supports), not on its declared class.

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Concept Made Simple

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“What is polymorphism and duck typing in Python?”

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Mind Map Answer

Polymorphism
same call, type-specific behavior
Duck typing
care about methods, not the class
Enabler
override methods (e.g. __str__, speak)
Formalize
ABCs / typing.Protocol

Learn by Doing

Hands-on Keyboard

python
class Dog:
    def speak(self): return "Woof"
class Cat:
    def speak(self): return "Meow"

def announce(animal):        # no type check
    print(animal.speak())    # works if it has speak()

for a in (Dog(), Cat()):
    announce(a)
Output
Woof
Meow

Think Beyond the Expected

What If?

How does duck typing differ from Java-style interfaces?

Java checks types at compile time — an object must explicitly implement an interface. Python checks at runtime: if the object has the method you call, it works, regardless of its class or any declared interface. It's more flexible but shifts errors to runtime; typing.Protocol adds optional static checking.

Real World

Functions that accept 'any file-like object' or 'anything iterable' rely on duck typing — you can pass a real file, StringIO, or a custom class, and it just works as long as it has the needed methods.

Interviewer's Expectation

Keywords they're listening for:

  • same op, different types
  • duck typing = behavior over class
  • runtime not compile-time
  • method overriding
  • Protocol/ABC to formalize

Common Mistakes

  • Adding unnecessary isinstance() checks
  • Assuming compile-time interface guarantees
  • Ignoring the runtime-error risk of duck typing

Best Practices

  • Program to behavior, not concrete types
  • Use ABCs/Protocol where a contract must be explicit
  • Handle the missing-method case gracefully

Follow-up Questions

  1. How do abstract base classes fit in?
  2. What is typing.Protocol (structural typing)?
  3. How does operator overloading relate (e.g. __add__)?

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Plain-language foundations

I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner.

Topic: Polymorphism (Python)
Interview question: "What is polymorphism and duck typing in Python?"

Please:
1. Explain the core idea in simple, plain language, using an everyday analogy.
2. Define any technical terms you use.
3. Walk through one small, concrete example.
4. Finish with a single sentence I can easily remember.

Keep the tone friendly and assume I'm new to this topic.
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