Entry

Restricted list

Jul 5th, 2000 10:00
Nathan Wallace, unknown unknown, Hans Nowak, Snippet 134, Python Snippet Support Team

"""
Packages: basic_datatypes.lists;oop
"""
# restrictedlist.py
# A list which filters out certain elements.
from UserList import UserList
class RestrictedList(UserList):
    def append(self, x):
        if self.filter(x): UserList.append(self, x)
    def filter(self, obj):
        return 1
    def __add__(self, other):
        new_rl = self.__class__()   # !!!
        new_rl.data = self.data[:]
        try:
            # let's see if this is a sequence
            for item in other:
                new_rl.append(item)
        except:
            # it's not a sequence -- try to add this element
            new_rl.append(other)
        return new_rl
if __name__ == "__main__":
    class PositiveIntList(RestrictedList):
        def filter(self, x):
            if not type(x) in (type(1), type(1L)): return 0
            return x >= 0
    pil = PositiveIntList()
    pil = pil + [1, -2, 3.02, 'x', 5, 8, 9L, 2j]
    print pil