A simple, high accuracy counter (not appropriate for higher frequency usage [>1 update/sec for any key])

basic_counter.py

from google.appengine.ext import db


class Counter(db.Model):
    """Persistent storage of a counter's values"""
    # key_name is the counter's name
    value = db.IntegerProperty(indexed=False)

    @classmethod
    def get(cls, name):
        """Returns the value of the specified counter"""
        counter = cls.get_by_key_name(name)
        if not counter:
            return 0
        return counter.value

    @classmethod
    def incr(cls, name, delta=1):
        """Increments a counter"""
        def tx():
            counter = cls.get_by_key_name(name)
            if not counter:
                counter = Counter(key_name=name, value=0)
            counter.value += delta
            counter.put()
        db.run_in_transaction(tx)