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A key-value store with ordered traversal of keys

Project Description

Park is a persistent key-value API for Python with ordered traversal of keys. Both keys and values are binary safe. It’s similar in use to LevelDB, but has no dependencies outside the Python standard library.

It is meant to be extremely easy to use and can scale to a few gigabytes of data. It allows you to be lazy until it doesn’t meet your needs. Use it until then.

It supports simple getting and setting of byte data:

>>> kv = park.SQLiteStore("numbers.park")
>>> kv.put("1", "one")
>>> kv.put("2", "two")
>>> kv.put("3", "three")
>>> kv.put("4", "four")

>>> kv.get("2")

Batched setting of data from an iterable:

>>> kv.put_many([("1", "one"), ("2", "two"), ("3", "three")])

>>> kv.get("3")

Lexically ordered traversal of keys and items, with start and end sentinels (inclusive):

>>> kv.put("1", "one")
>>> kv.put("2", "two")
>>> kv.put("3", "three")
>>> kv.put("11", "eleven")
>>> kv.put("12", "twelve")

>>> list(kv.keys())
['1', '11', '12', '2', '3']

>>> list(kv.keys(key_from="12"))
['12', '2', '3']

>>> list(kv.keys(key_from="12", key_to="2"))
['12', '2']

>>> list(kv.items(key_from="12"))
[('12', 'twelve'), ('2', 'two'), ('3', 'three')]

Iteration over all keys or items with a given prefix:

>>> kv.put("pet/dog", "Canis lupus familiaris")
>>> kv.put("pet/cat", "Felis catus")
>>> kv.put("pet/wolf", "Canis lupus")

>>> list(kv.prefix_keys("pet/"))
['pet/cat', 'pet/dog', 'pet/wolf']

>>> list(kv.prefix_keys("pet/", strip_prefix=True))
['cat', 'dog', 'wolf']

>>> list(kv.prefix_items("pet/", strip_prefix=True))
[('cat', 'Felis catus'),
 ('dog', 'Canis lupus familiaris'),
 ('wolf', 'Canis lupus')]

It plays well with generators, so you can e.g. park all the counting numbers (this will take a while):

def numbers():
    for num in itertools.count(1):
        key = value = str(num)
        yield key, value


Or recursively park a directory’s contents (keyed by relative paths) from the local filesystem:

def file_item(filename):
    with open(filename, "r") as fd:
        return filename,

kv.put_many(file_item(os.path.join(root, name))
            for root, dirs, files in os.walk(directory)
            for name in files)

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Source None Sep 6, 2012

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