Default values in constructors in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a constructor in Python classes?

A constructor is a special method named __init__ that runs when you create a new object from a class. It sets up the object’s initial state.

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How do you set a default value for a constructor parameter in Python?

You assign a value to the parameter in the __init__ method like def __init__(self, name='Guest'):. If no argument is given, the default is used.

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Why use default values in constructors?

Default values let you create objects without giving all details every time. This makes your code simpler and more flexible.

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What happens if you call a constructor without a parameter that has a default value?

The constructor uses the default value for that parameter automatically.

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Show a simple example of a Python class with a constructor that has a default value.

Example:<br><pre>class Person:
    def __init__(self, name='Guest'):
        self.name = name

p1 = Person()
print(p1.name)  # Output: Guest

p2 = Person('Alice')
print(p2.name)  # Output: Alice</pre>

What is the purpose of a default value in a constructor parameter?

A To make the constructor private

B To provide a value if no argument is passed

C To force the user to pass a value

D To delete the parameter

Default values provide a fallback value when no argument is given during object creation.

How do you define a default value for a parameter in Python's __init__ method?

A def __init__(self, param=default):

B def __init__(self, param): param = default

C def __init__(self, param): return default

D def __init__(self, param?=default):

You assign the default value directly in the parameter list.

What will print(p.name) output if p = Person() and def __init__(self, name='Guest')?

A Error

B None

C Guest

D Empty string

Since no name is passed, the default 'Guest' is used.

Can you have multiple parameters with default values in a constructor?

A Defaults are not allowed in constructors

B No, only one parameter can have a default

C Only the first parameter can have a default

D Yes, all can have defaults

You can assign default values to as many parameters as you want.

What happens if you call Person('Bob') when def __init__(self, name='Guest')?

A The name 'Bob' is used instead of the default

B The default 'Guest' is used anyway

C An error occurs

D The constructor ignores the argument

The passed argument overrides the default value.

Explain how default values in constructors help when creating objects.

Think about what happens if you don't pass some values when making an object.

Write a simple Python class with a constructor that has two parameters, one with a default value.

Use <code>def __init__(self, param1, param2=default):</code> format.