如何提取两个字符之间的子字符串？

Question

I want to extract all the dates inside my_list

my_list = ['FRE_5F_20200915-08u21m57s_ab', 'AY_C7_20200813-17u02m16s_ab', 'ALL_20200915-06u34m05s_ab', 'FF_20200816-11u21m44s_ab']

This is my code:

for file in my_list:
    find = re.search('_(.+?)-', file).group(1)
    print(find)

This is the output:

5F_20200915
C7_20200813
20200915
20200816

This is my expected output:

20200915
20200813
20200915
20200816

Answer 1

You can use _(\\d+)- Regex101 :

import re


my_list = ['FRE_5F_20200915-08u21m57s_ab', 'AY_C7_20200813-17u02m16s_ab', 'ALL_20200915-06u34m05s_ab', 'FF_20200816-11u21m44s_ab']
r = re.compile(r'_(\d+)-')

for s in my_list:
    m = r.search(s)
    if m:
        print(m.group(1))

Prints:

20200915
20200813
20200915
20200816

Answer 2

Fixed your regex, your output matches your regex. To only match numbers between _ and - you can use '_(\\d+)-' as seen below

import re
my_list = ['FRE_5F_20200915-08u21m57s_ab', 'AY_C7_20200813-17u02m16s_ab', 'ALL_20200915-06u34m05s_ab', 'FF_20200816-11u21m44s_ab']
for file in my_list:
    find = re.search('_(\d+)-', file).group(1)
    print(find)

Which results in

20200915
20200813
20200915
20200816

Answer 3

This can be done without a regex:

for s in my_list:

    # find the index of -
    index = s.index("-")

    # extract 8 characters before that
    print(s[index-8:index])