Question

I just found the pattern matching feature in Racket very powerful.

> (match '(1 2 3) [(list a b c) (list c b a)])

'(3 2 1)

> (match '(1 2 3) [(list 1 a ...) a])

'(2 3)

> (match '(1 2 3)
    [(list 1 a ..3) a]
    [_ 'else])

'else

> (match '(1 2 3 4)
    [(list 1 a ..3) a]
    [_ 'else])

'(2 3 4)

> (match '(1 2 3 4 5)
    [(list 1 a ..3 5) a]
    [_ 'else])

'(2 3 4)

> (match '(1 (2) (2) (2) 5)
    [(list 1 (list a) ..3 5) a]
    [_ 'else])

'(2 2 2)

Is there similar syntax sugar or library to do that in Python?

Answer 1

No there is not, python’s pattern matching is only iterable unpacking like this:

>>> (x, y) = (1, 2)
>>> print x, y
1 2

Or in function definition:

>>> def x((x, y)):
    ...

Or in python 3:

>>> x, *y = (1, 2, 3)
>>> print(x)
1
>>> print(y)
[2, 3]

But there are some of external libraries that realize pattern matching.