我正在编写一个脚本，需要在启动时处理一个相当大的（62万字）词典。输入词典逐字处理为defaultdict(list)，键为字母bi和三字符，值为包含关键字母n-gram的单词列表
for word in lexicon_file:
word = word.lower()
for letter n-gram in word:
lexicon[n-gram].append(word)
，例如
> lexicon["ab"]
["abracadabra", "abbey", "abnormal"]
结果结构包含25 000个键，每个键包含一个列表，其中包含1到133 000个字符串（平均值为500，中位数为20）。所有字符串均采用windows-1250编码。
这个处理需要花费很多时间（考虑到脚本的预期实际运行时间可以忽略不计，但通常在测试时会产生负担）并且由于词典本身永远不会改变，我认为序列化生成的defaultdict(list)可能会更快然后在每次后续启动时反序列化它。
我发现即使使用cPickle，反序列化过程的速度也只是处理词典的两倍，平均值接近：
> normal lexicon creation
45 seconds
> cPickle deserialization
80 seconds
我没有任何序列化方面的经验，但我希望反序列化比正常处理更快，至少对于cPickle模块而言。
我的问题是，这个结果可以预期吗？为什么？有没有办法更快地存储/加载我的结构？
答案 0 :(得分：2)
想出这样的事情的最好方法是编写一堆测试并使用timeit来查看哪个更快。我在下面进行了一些测试，但你应该用你的词典来尝试这个，因为你的结果可能会有所不同。
如果您希望时间更稳定（准确），可以将number参数增加到timeit - 它只会让测试花费更长时间。另请注意，timeit返回的值是总执行时间，而不是每次运行的时间。
testing with 10 keys...
serialize flat: 2.97198390961
serialize eval: 4.60271120071
serialize defaultdict: 20.3057091236
serialize dict: 20.2011070251
serialize defaultdict new pickle: 14.5152060986
serialize dict new pickle: 14.7755970955
serialize json: 13.5039670467
serialize cjson: 4.0456969738
unserialize flat: 1.29577493668
unserialize eval: 25.6548647881
unserialize defaultdict: 10.2215960026
unserialize dict: 10.208122015
unserialize defaultdict new pickle: 5.70747089386
unserialize dict new pickle: 5.69750404358
unserialize json: 5.34811091423
unserialize cjson: 1.50241613388
testing with 100 keys...
serialize flat: 2.91076397896
serialize eval: 4.72978711128
serialize defaultdict: 21.331786871
serialize dict: 21.3218340874
serialize defaultdict new pickle: 15.7140991688
serialize dict new pickle: 15.6440980434
serialize json: 14.3557379246
serialize cjson: 5.00576901436
unserialize flat: 1.6677339077
unserialize eval: 22.9142649174
unserialize defaultdict: 10.7773029804
unserialize dict: 10.7524499893
unserialize defaultdict new pickle: 6.13370203972
unserialize dict new pickle: 6.18057107925
unserialize json: 5.92281794548
unserialize cjson: 1.91151690483
代码：
import cPickle
import json
try:
import cjson # not Python standard library
except ImportError:
cjson = False
from collections import defaultdict
dd1 = defaultdict(list)
dd2 = defaultdict(list)
for i in xrange(1000000):
dd1[str(i % 10)].append(str(i))
dd2[str(i % 100)].append(str(i))
dt1 = dict(dd1)
dt2 = dict(dd2)
from timeit import timeit
def testdict(dd, dt):
def serialize_defaultdict():
with open('defaultdict.pickle', 'w') as f:
cPickle.dump(dd, f)
def serialize_p2_defaultdict():
with open('defaultdict.pickle2', 'w') as f:
cPickle.dump(dd, f, -1)
def serialize_dict():
with open('dict.pickle', 'w') as f:
cPickle.dump(dt, f)
def serialize_p2_dict():
with open('dict.pickle2', 'w') as f:
cPickle.dump(dt, f, -1)
def serialize_json():
with open('dict.json', 'w') as f:
json.dump(dt, f)
if cjson:
def serialize_cjson():
with open('dict.cjson', 'w') as f:
f.write(cjson.encode(dt))
def serialize_flat():
with open('dict.flat', 'w') as f:
f.write('\n'.join([' '.join([k] + v) for k, v in dt.iteritems()]))
def serialize_eval():
with open('dict.eval', 'w') as f:
f.write('\n'.join([k + '\t' + repr(v) for k, v in dt.iteritems()]))
def unserialize_defaultdict():
with open('defaultdict.pickle') as f:
assert cPickle.load(f) == dd
def unserialize_p2_defaultdict():
with open('defaultdict.pickle2') as f:
assert cPickle.load(f) == dd
def unserialize_dict():
with open('dict.pickle') as f:
assert cPickle.load(f) == dt
def unserialize_p2_dict():
with open('dict.pickle2') as f:
assert cPickle.load(f) == dt
def unserialize_json():
with open('dict.json') as f:
assert json.load(f) == dt
if cjson:
def unserialize_cjson():
with open('dict.cjson') as f:
assert cjson.decode(f.read()) == dt
def unserialize_flat():
with open('dict.flat') as f:
dtx = {}
for line in f:
vals = line.split()
dtx[vals[0]] = vals[1:]
assert dtx == dt
def unserialize_eval():
with open('dict.eval') as f:
dtx = {}
for line in f:
vals = line.split('\t')
dtx[vals[0]] = eval(vals[1])
assert dtx == dt
print 'serialize flat:', timeit(serialize_flat, number=10)
print 'serialize eval:', timeit(serialize_eval, number=10)
print 'serialize defaultdict:', timeit(serialize_defaultdict, number=10)
print 'serialize dict:', timeit(serialize_dict, number=10)
print 'serialize defaultdict new pickle:', timeit(serialize_p2_defaultdict, number=10)
print 'serialize dict new pickle:', timeit(serialize_p2_dict, number=10)
print 'serialize json:', timeit(serialize_json, number=10)
if cjson:
print 'serialize cjson:', timeit(serialize_cjson, number=10)
print 'unserialize flat:', timeit(unserialize_flat, number=10)
print 'unserialize eval:', timeit(unserialize_eval, number=10)
print 'unserialize defaultdict:', timeit(unserialize_defaultdict, number=10)
print 'unserialize dict:', timeit(unserialize_dict, number=10)
print 'unserialize defaultdict new pickle:', timeit(unserialize_p2_defaultdict, number=10)
print 'unserialize dict new pickle:', timeit(unserialize_p2_dict, number=10)
print 'unserialize json:', timeit(unserialize_json, number=10)
if cjson:
print 'unserialize cjson:', timeit(unserialize_cjson, number=10)
print 'testing with 10 keys...'
testdict(dd1, dt1)
print 'testing with 100 keys...'
testdict(dd2, dt2)