cull_list.py

"""
>>> from copy import deepcopy
>>> pred = lambda v: v <= 2
>>> test_list = [1, 2, 1, 3, 1, 2, 4, 2, 3, 1]
>>> correct = [1, 2, 1, 1, 2, 2, 1]
... # the values from the list which are less than or equal to 2

>>> def dotest(cull, lst, pred):
...     lst = deepcopy(lst)
...     cull(lst, pred)
...     return lst

>>> dotest(shawley_cull_list, test_list, pred)
[1, 2, 1, 1, 2, 2, 1]

>>> dotest(cull_list, test_list, pred)
[1, 2, 1, 1, 2, 2, 1]

>>> pred = lambda v: v > 2
>>> correct = [3, 4, 3] # The values from the list that are greater than 2

>>> dotest(shawley_cull_list, test_list, pred)
[2, 3, 2, 4, 3]

>>> dotest(cull_list, test_list, pred)
[3, 4, 3]
>>> dotest(genexp_cull_list, test_list, pred)
[3, 4, 3]

>>> dotest(user_cull_list, test_list, pred)
[3, 2, 4, 2, 3]

>>> test_list = [1, 2, 3, 4, 5, 6]
>>> pred = lambda v: v <= 2
>>> dotest(shawley_cull_list, test_list, pred)
[1, 2, 4, 6]
>>> dotest(user_cull_list, test_list, pred)
[1, 2, 4, 6]
>>> dotest(cull_list, test_list, pred)
[1, 2]
>>> dotest(efficient_cull_list, test_list, pred)
[1, 2]
>>> dotest(genexp_cull_list, test_list, pred)
[1, 2]
"""

def shawley_cull_list(lst, my_predicate):
    for idx, val in enumerate(lst):
        if not my_predicate(val):
            del(lst[idx])

def cull_list(lst, pred):
    """Removes all values from ``lst`` which for which ``pred(v)`` is false."""
    def remove_all(v):
        """Remove all instances of ``v`` from ``lst``"""
        try:
             while True:
                 lst.remove(v)
        except ValueError:
             pass

    values = set(lst)

    for v in values:
        if not pred(v):
            remove_all(v)

def user_cull_list(lst, pred):
    for n, x in enumerate(lst):
        if not pred(x): lst.remove(x)

def efficient_cull_list(lst, pred):
    end = len(lst)
    i = 0
    while i < end:
        if not pred(lst[i]):
            del lst[i]
            end -= 1
        else:
            i += 1

def genexp_cull_list(lst, pred):
    lst[:] = (v for v in lst if pred(v))