Enforce items at beginning and end of list

Question

How can I modify this list so that all p\'s appear at the beginning, the q\'s at the end, and the values in between are sorted alphabetically?

Answer 1

One idea is to use a priority dictionary with a custom function. This is naturally extendable should you wish to include additional criteria.

L = ['f','g','p','a','p','c','b','q','z','n','d','t','q']

def sort_func(x):
    priority = {'p': 0, 'q': 2}
    return priority.get(x, 1), x

res = sorted(L, key=sort_func)

print(res)

['p', 'p', 'a', 'b', 'c', 'd', 'f', 'g', 'n', 't', 'z', 'q', 'q']