Python 字符串替换效率 replace＞ re.sub

• 单纯的替换，正则的效率比 replace 低三倍左右
• 那什么时候正则的效率比 replace 高呢？

import re,timeit
str = "abcdefghigkqpwueriwutghlskajdf,mnbz,xcnvoiequynf12341234321065498+7mnbz,xcnvoiequynf12341234321065498+7mnbz,xcnvoiequynf12341234321065498+7mnbz,xcnvoiequynf12341234321065498+7"

# pattern1
start = timeit.default_timer()
for i in range(1000000):
    tst = re.sub("mn|123|[abcdef7]", "", str)
stop = timeit.default_timer()
print('pattern1', 'Time: ', stop - start)

# pattern2
start = timeit.default_timer()
for i in range(1000000):
    tst = str.replace("mn", "")
    tst = tst.replace("123", "")
    tst = tst.replace("a", "")
    tst = tst.replace("b", "")
    tst = tst.replace("c", "")
    tst = tst.replace("d", "")
    tst = tst.replace("e", "")
    tst = tst.replace("f", "")
    tst = tst.replace("7", "")

stop = timeit.default_timer()
print('pattern2', 'Time: ', stop - start)

# pattern3
start = timeit.default_timer()
for i in range(1000000):
    tst = re.sub("mn", "", str)
stop = timeit.default_timer()
print('pattern3', 'Time: ', stop - start)

# pattern4
start = timeit.default_timer()
for i in range(1000000):
    tst = str.replace("mn", "")

stop = timeit.default_timer()
print('pattern4', 'Time: ', stop - start)
# 输出
# pattern1 Time:  10.851562640495892
# pattern2 Time:  4.726493571613192
# pattern3 Time:  1.5144934460814898
# pattern4 Time:  0.5535754144044809