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utils.py
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utils.py
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import collections
import msgpack
import os
import json
from msgpack.exceptions import OutOfData
MAX_MSGPACK_ARRAY_HEADER_LEN = 5
class PersistentDict(collections.UserDict):
def __init__(self, path=None, data={}):
if os.path.isfile(path):
with open(path, 'r') as f:
data = json.loads(f.read())
self.path = path
super().__init__(data)
def __setitem__(self, key, value):
self.data[self.__keytransform__(key)] = value
self.persist()
def __delitem__(self, key):
del self.data[self.__keytransform__(key)]
self.persist()
def __keytransform__(self, key):
return key
def persist(self):
with open(self.path, 'w+') as f:
f.write(json.dumps(self.data))
def msgpack_appendable_pack(o, path):
open(path, 'a+').close() # touch
with open(path, 'r+b') as f:
packer = msgpack.Packer()
unpacker = msgpack.Unpacker(f)
if type(o) == list:
try:
previous_len = unpacker.read_array_header()
except OutOfData:
previous_len = 0
header = packer.pack_array_header(previous_len + len(o))
f.seek(0)
f.write(header)
f.write(bytes(1) * (MAX_MSGPACK_ARRAY_HEADER_LEN - len(header)))
f.seek(0, 2)
for element in o:
f.write(packer.pack(element))
else:
f.write(packer.pack(o))
def msgpack_appendable_unpack(path):
# if not list
# return msgpack.unpackb(f.read())
with open(path, 'rb') as f:
packer = msgpack.Packer()
unpacker = msgpack.Unpacker(f, encoding='utf-8')
length = unpacker.read_array_header()
header_length_bin = len(packer.pack_array_header(length))
unpacker.read_bytes(MAX_MSGPACK_ARRAY_HEADER_LEN - header_length_bin)
f.seek(MAX_MSGPACK_ARRAY_HEADER_LEN)
return [unpacker.unpack() for _ in range(length)]