为什么在某些情况下,Python 3中的连接似乎比Python 2中的连接慢？
影响最大的串联方法似乎是字节对象的连续串联,从O(n)到O(n?)操作.
我的分析代码大部分在这里：
#!/usr/bin/env python
from operator import concat
from sys import version, version_info
from timeit import timeit # Compatibility: ver >= 2.6
# ver = version.partition('
')[0].rstrip()
ver = '.'.join(str(v) for v in version_info[:3])
print(ver)
if version_info[0] == 2:
from StringIO import StringIO
else:
from io import StringIO
from functools import reduce
xrange = range
def build_plus():
output = ''
for _ in xrange(input_len):
output += 'a'
return output
def build_join():
return ''.join('a' for _ in xrange(input_len))
def build_bytes_plus():
output = b''
for _ in xrange(input_len):
output += b'a'
return output
def build_stringio():
output = StringIO()
for _ in xrange(input_len):
output.write('a')
return output.getvalue()
def build_reduce():
return reduce(concat, ('a' for _ in xrange(input_len)))
builds = {'str+': build_plus,
'join': build_join,
'reduce': build_reduce,
'bytes+': build_bytes_plus,
'StringIO': build_stringio}
if version_info[0] == 2:
import cStringIO
def build_cstringio():
output = cStringIO.StringIO()
for _ in xrange(input_len):
output.write('a')
return output.getvalue()
builds['cStringIO'] = build_cstringio
else:
from io import BytesIO
def build_bytesio():
output = BytesIO()
for _ in xrange(input_len):
output.write(b'a')
return output.getvalue()
builds['BytesIO'] = build_bytesio
resfile = open('times.csv', 'a')
size_range = 50 # Number of points over the size axis
min_order = 1.0 # 10^x byte input min
max_order = 5.0 # 10^x byte input max
for allow_gc in (False, True):
setup = 'gc.enable()' if allow_gc else 'pass'
for build_name, build_fun in builds.items():
# For a roughly constant confidence interval, aim for uniform sample density across the
# (logarithmic) input size axis.
for size_index in range(size_range+1):
input_len = int(10**((max_order-min_order)*size_index/size_range + min_order))
# Rather than repeating many measurements at one input size, perform one measurement
# per input size for a continuous range of input sizes and apply smoothing later.
dur = timeit(build_fun, setup, number=1)
resfile.write('"%s",%s,"%s",%d,%.6g
' % (ver, str(allow_gc).upper(), build_name,
input_len, dur))
我的R脚本中的一些图形如下所示：
