What is functools.cmp_to_key in Python?

What is the functools module in Python?

The functools module in Python allows us to create higher-order functions that interact with other functions. The higher-order functions either return other functions or operate on them to broaden the scope of the function without modifying or explicitly defining them.

Key function

A callable that returns a value for sorting or ordering is known as a key function or a collation function. A lot of Python functions accept key functions to modify the order or grouping of items. For example, min(), max() etc. A key function takes an argument and returns a value that’s considered as the sort key.

Comparison function

Any callable that performs the following is called a comparison function.

1. Accepts two arguments.
2. Compares the two arguments.
3. Returns
   1. A negative value indicating the first argument is lesser than the second argument.
   2. A positive value indicating the first argument is greater than the second argument.
   3. A zero indicates the first argument is equal to the second argument.

cmp_to_key function

Python 2 that has reached End of Life supported comparison functions. But now, the comparison functions are deprecated and no longer used. Hence, cmp_to_key is introduced in Python 3 to support the comparison functions in the form of key functions.

Syntax

functools.cmp_to_key(callable)

The function takes a callable as a parameter.

Code

Code explanation

• Lines 1–3: We import the relevant classes and functions.
• Lines 6–8: We define a comparison function called compare.
• Line 11: A list of random values ranging from 10 to 30 is generated. The generated list is called randomlist.
• Line 12:randomlist is printed before sorting.
• Line 15: randomlist is sorted using the sort() method, passing the compare function as the parameter to cmp_to_key.
• Line 16: The sorted randomlist is printed.