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01. Define a function that adds two numbersE02. Write a function that returns a greetingE03. Implement a function to find the maximum of threeE04. Create a function to join words with a separatorE05. Write a function that returns the length of a sequenceE06. Implement a function with a default argumentE07. Create a function that accepts any number of argsE08. Write a function that handles keyword argumentsE09. Implement a function that returns multiple valuesE10. Write a function that modifies a passed listE11. Define a function that reads a global variableE12. Write a function with a simple docstringE13. Write a function that demonstrates nonlocal usageM14. Create a function factory returning customized functionsM15. Implement argument unpacking with *args and **kwargsM16. Write a function that avoids mutable default argsM17. Create a function with keyword-only parametersM18. Implement a simple recursive function with a base caseM19. Implement a decorator that logs function callsH20. Write a decorator that memoizes function resultsH

Problem No 13

Write a function that demonstrates nonlocal usage

Medium

≈ 14 minute session

Back to curriculumNext lesson

Summary

Learn how to use the nonlocal keyword by creating a closure that keeps internal state across calls.

Problem statement

Write a function create_counter() that returns another function (a counter). Each time the returned counter function is called, it should increment an internal count and return the new value. Use the nonlocal keyword to modify the count from inside the nested function. The first call to a fresh counter should return 1.

Task

Implement create_counter() that returns a function using a nonlocal variable to track and increment a counter each time the returned function is called.

Examples

Single call on a new counter

Input

create_counter()()

Output

1

Explanation

create_counter() returns a new counter function. Calling it once increments the internal count from 0 to 1 and returns 1.

Multiple calls on the same counter

Input

(lambda c: (c(), c(), c()))(create_counter())

Output

(1, 2, 3)

Explanation

The lambda creates one counter, calls it three times in sequence, and returns the tuple of results showing the nonlocal state incrementing.

Input format

Each test calls the functions directly as expressions, e.g., create_counter()(), or uses a temporary variable via a lambda to call multiple times.

Output format

Return values from the evaluated expression. For example "1" or a tuple representation like "(1, 2)".

Constraints

- Use nonlocal to modify the enclosed count variable. - The returned counter must start counting at 1 on its first call. - Do not use global variables. - The counter should be independent per create_counter() call.

Samples

Sample input 0

(lambda c: (c(), c()))(create_counter())

Sample output 0

(1, 2)

Explanation 0

Two calls on the same counter produce 1 then 2.

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