Basic instance check
Input
is_instance(B(), A)
Output
True
B is a subclass of A, so an instance of B is an instance of A.
Full lesson preview
Check isinstance and issubclass Relations
Learn to correctly determine instance and subclass relationships and handle invalid inputs safely.
Python practice8 minInheritance & PolymorphismBeginnerLast updated April 8, 2026
Problem statement
You'll implement two helper functions that mirror Python's isinstance and issubclass behavior but are safe: they should return True/False and never raise an exception when given invalid argument types. The learning goal is to understand how isinstance and issubclass behave and to practice defensive checks when working with dynamic inputs.
Implement:
- is_instance(obj, class_or_tuple): Returns True if obj is an instance of class_or_tuple (like isinstance). If class_or_tuple is not a class or a tuple of classes, return False.
- is_subclass(child, parent): Returns True if child is a subclass of parent (like issubclass). If either argument is not a class (or a tuple of classes where appropriate), return False.
A small class hierarchy is provided for testing. Your functions must not raise exceptions when passed invalid types; instead return False.
Task
Implement safe wrappers for isinstance and issubclass that return False instead of raising on invalid input types.
Examples
Input format
Single function call expression. Examples: is_instance(obj, cls) or is_subclass(child, parent).
Output format
Boolean result (True or False). The test harness compares str(return_value) to the expected string.
Constraints
Do not raise exceptions for invalid inputs; return False instead. Do not import external libraries.
Samples
Sample 1
Input
is_subclass(C, A)
Output
True
C inherits from B which inherits from A.