IndexedFile

This is a simple implementation of Indexed files similar, but not identical, to dbm/gdbm/ndbm.

Usage

Instantiation:

from indexed import IndexedFile

db = IndexedFile("database.db", "c")

Store some data. Keys must be hashable objects, and the content can only be bytes:

db[("IDENT", 405)] = b"this is info to be stored"
db[35] = json.dumps({ "name": "Phil", 
                      "address": "35, Barnacle st.", 
                      "date_of_birth": "1982/11/24"}).encode()

Retrieve data:

print(db[("IDENT", 405)])  # prints b'this is info to be stored'

Bad keys throw KeyError exception:

db["badkey"]   # KeyError: 'badkey'

the .keys(), .values() and .items() methods behave like in dictionaries, and the objects are iterable. Iterating over an IndexedFile gives the keys in any order:

for key in db:
   print(key, end=" ")  # prints 35 ("IDENT", 405)

Using .close() method closes the object and it cannot be used further. To use after .close(), a new instance should be created.

db.close()

The objects are context managers:

with IndexedFile("database.db", "r") as db:
	print(db[35])

Reference

IndexedFile(name, mode='r', recordsize=DEFAULT_RECORD_SIZE, num_recs_hint=DEFAULT_NUM_RECORDS)

Create a new IndexedFile object, where name is the filename to store it to, mode is either 'c' which creates or resets a new file, or 'r' which opens an existing file.

recordsize is the size of each record. Data items can be bigger than the recordsize, in which case a suitable number of records will be allocated to contain the object.

num_recs_hint is the number of free records initially allocated. When more records are needed than are available the file will be resized to double its size.

recordsize and num_recs_hint, if specified, are ignored on mode 'r'.

IndexedFile.close()

Closes access to the IndexedFile. The file cannot be re-opened. In order to access the file after .close() a new instance should be created with mode 'r'

IndexedFile.keys()

Returns an iterable that gives the keys in sequence

IndexedFile.values()

Returns an iterable that gives the values in sequence

IndexedFile.items()

Returns and iterable that gives tuples of the form (key, value)

License

This software is released under the MIT License