utils.py

class ItemsCount(object):
    def __init__(self, value):
        self._value = value

    def __call__(self, sequence):
        if isinstance(self._value, (bytes, str,)):
            if self._value.endswith("%"):
                total_count = len(sequence)
                percentage = int(self._value[:-1])
                # at least one sentence should be chosen
                count = max(1, total_count*percentage // 100)
                return sequence[:count]
            else:
                return sequence[:int(self._value)]
        elif isinstance(self._value, (int, float)):
            return sequence[:int(self._value)]
        else:
            ValueError("Unsuported value of items count '%s'." % self._value)

    def __repr__(self):
        return to_string("<ItemsCount: %r>" % self._value)