Level 6Exercise #149

Flatten arbitrary nesting

Flatten arbitrarily nested lists while treating every non-list value as atomic.

What you’ll practice

This Level 6 exercise focuses on recursion + isinstance in the Professional curriculum. Solve the challenge prompt above using clear, idiomatic Python and the relevant language or standard-library tools.

Relevant Python reference: re — Regular expression operations.

Sample Test Cases

Example #1

Input:flatten([1,[2,[3,4]],5])

Output:[1,2,3,4,5]

Reference Solution

Reveal Reference Solution

def flatten(values: list) -> list:
    result = []
    def visit(value):
        if isinstance(value, list):
            for item in value: visit(item)
        else:
            result.append(value)
    visit(values)
    return result

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Flatten arbitrary nesting

What you’ll practice

Sample Test Cases

Further Reading

Reference Solution