Source: 📖 Effective Python item 25

Positional-only arguments explained

Positional-only arguments can be passed in only by position, not by keyword. You can employ these in function definitions by using the / symbol to indicate when positional-only arguments end.

def my_function(first, last, /, middle=None):
	if middle:
		print(f'{first} {middle} {last})
	else:
		print(f'{first} {last}')

When calling the above functions, any attempt to provide the first or last arguments by keyword will raise an exception.

See also:

• Keyword-only arguments explained