def strTest(num):
  s = 'Hello'
  for i in range(num):
    s += 'x'
  return s

def strTest2(num):
  s = 'Hello'
  l = list(s)
  for i in range(num):
    l.append('x')
  return ''.join(l)

> def strTest1(num):
...   s = 'Hello'
...   for i in range(num):
...     s += 'x'
...   return s
> def strTest2(num):
...   s = 'Hello'
...   l = list(s)
...   for i in range(num):
...     l.append(s)
...   return ''.join(l)
>
> from timeit import timeit
# 运行10万级别数据，运行速度比对
> timeit("strTest1(100000)", setup="from __main__ import strTest1", number=1)
0.016680980406363233
> timeit("strTest2(100000)", setup="from __main__ import strTest2", number=1)
0.009688869110618725
# 运行100万级别数据，运行速度比对
> timeit("strTest1(1000000)", setup="from __main__ import strTest1", number=1)
0.14558920607187195
> timeit("strTest2(1000000)", setup="from __main__ import strTest2", number=1)
0.1335057276853462
# 运行1000万级别数据，运行速度比对
> timeit("strTest1(10000000)", setup="from __main__ import strTest1", number=1)
5.9497953107860475
> timeit("strTest2(10000000)", setup="from __main__ import strTest2", number=1)
1.3268972136649921
# 运行2000万级别数据，运行速度比对
> timeit("strTest1(20000000)", setup="from __main__ import strTest1", number=1)
21.661270140499056
> timeit("strTest2(20000000)", setup="from __main__ import strTest2", number=1)
2.6981786518920217
# 运行3000万级别数据，运行速度比对
> timeit("strTest1(30000000)", setup="from __main__ import strTest1", number=1)
49.858089123966295
> timeit("strTest2(30000000)", setup="from __main__ import strTest2", number=1)
4.285787770209481
# 运行4000万级别数据，运行速度比对
> timeit("strTest1(40000000)", setup="from __main__ import strTest1", number=1)
86.67876273457563
> timeit("strTest2(40000000)", setup="from __main__ import strTest2", number=1)
5.328653452047092
# 运行5000万级别数据，运行速度比对
> timeit("strTest1(50000000)", setup="from __main__ import strTest1", number=1)
130.59138063819023
> timeit("strTest2(50000000)", setup="from __main__ import strTest2", number=1)
6.8375931077291625
# 运行6000万级别数据，运行速度比对
> timeit("strTest1(60000000)", setup="from __main__ import strTest1", number=1)
188.28227241975003
> timeit("strTest2(60000000)", setup="from __main__ import strTest2", number=1)
8.080144489401846
# 运行7000万级别数据，运行速度比对
> timeit("strTest1(70000000)", setup="from __main__ import strTest1", number=1)
256.54383904350277
> timeit("strTest2(70000000)", setup="from __main__ import strTest2", number=1)
9.387400816458012
# 运行8000万级别数据，运行速度比对
> timeit("strTest1(80000000)", setup="from __main__ import strTest1", number=1)
333.7185806572388
> timeit("strTest2(80000000)", setup="from __main__ import strTest2", number=1)
10.946627677462857