Basic usage
Input
inc, dec, get = make_counter(10, 2) inc() get()
Output
12 12
Starting at 10 with step 2, inc() moves the counter to 12 and returns 12; get() returns the current value 12.
Full lesson preview
Build an Increment Decrement Counter Factory
Create a closure-based counter factory that returns increment, decrement and getter functions sharing the same state.
Python practice14 minClosures & Function FactoriesIntermediateLast updated April 13, 2026
Problem statement
Implement make_counter(start=0, step=1) which returns a tuple (inc, dec, get). inc() increments the shared counter by step and returns the new value. dec() decrements the counter by step and returns the new value. get() returns the current value without modifying it. The counter's state must be captured in a closure (no global variables).
Task
Learn to use closures to encapsulate mutable state and build simple function factories that produce stateful operations.
Examples
Input format
A single call to make_counter(...) and then calling the returned functions. Tests will call the functions returned by make_counter in a single expression.
Output format
The functions inc and dec return integers representing the updated counter; get returns the current integer value.
Constraints
start and step will be integers. You must use a closure to keep the counter state (use of global variables is not allowed). Returned object must be a tuple (inc, dec, get) where each element is a callable.
Samples
Sample 1
Input
make_counter(0, 1)[0]()
Output
1
Counter starts at 0; inc() with step 1 returns 1.