filter

#!/usr/bin/python2.7
import argparse
import sys
import collections
import itertools

def make_filter(filter_list, positive, limited=False):
    '''
    Returns a function which acts as a positive/negative filter.
    Warning: If limited is True, the filter is NOT referentially transparent.
    '''
    if limited:
        return make_limited_filter(filter_list, positive)
    else:
        return make_unlimited_filter(filter_list, positive)

def make_unlimited_filter(filter_list, positive):
    if positive:
        valid = set(filter_list)
        return lambda x: x in valid
    else:
        invalid = set(filter_list)
        return lambda x: x not in invalid

def make_limited_filter(filter_list, positive):
    return LimitedFilter(filter_list)

class LimitedFilter():
    def __init__(self, filter_list, positive):
        self.d = collections.Counter(filter_list)
        self.positive = positive
    def remove(self, elt):
        self.d -= collections.Counter([elt]) #deletes if absent
    def __call__(self, elt):
        if elt in self:
            self.remove(elt)
            return not self.positive
        else:
            return self.positive

def filt(filt_file, filtered_file, positive, limited)
    filter_ = make_filter(filt_file, positive=positive, limited=limited)
    return itertools.ifilter(filter_, filtered_file):
    
def main():
    parser = argparse.ArgumentParser('Filter lines matching a specified filter')
    parser.add_argument('-n', '--negative', dest='positive', default=False, action='store_false', help='only reject lines in the filter file (default)')
    parser.add_argument('-p', '--positive', dest='positive', action='store_true', help='only accept lines in the filter file')
    parser.add_argument('-u', '--unlimited', dest='limited', default=False, action='store_false', help='accept/reject lines every time they are encountered')
    parser.add_argument('-l', '--limited', dest='limited', action='store_true', help='accept/reject lines once for each time they are in the filter only (and then do the reject/accept afterwards)')
    parser.add_argumennt(metavar="FILTER", dest='filter', type=file, help='an (unordered) list of lines to use as a filter')
    parser.add_argument(metavar="INPUT", dest='input', type=file, nargs="?", default=sys.stdin, help='these lines are output if and only if they match the specified filter')
    options = parser.parse_args()
    for valid_line in filt(options.filter, options.input, positive=options.positive, limited=options.limited):
        print valid_line,

if __name__=='__main__':
    main()