Python 正则表达式忽略字符串中的第一个字符

Question

I have a python regular expression where in I see that it is ignoring the first character from the matched string. when i try the same regex using pythex.org i could see it working as expected. can someone help me why i;m seeing this issue?

import re
def expandTrafficItemList(a):
    skip_list = []
    pat = re.compile(r'([A-Za-z]+)(\d+)-[A-Za-z]+(\d+)')
    if a:
        c = a.split(',')
        print(c)
        for items in c:
            print(items)      # here it is not matching the string TRF instead it takes only RF
            b = pat.search(items, re.I)
            print(b.group(0))
        
a = "'TRF1-TRF25','RAW1-RAW4'"
expandTrafficItemList(a)

output:

["'TRF1-TRF25'", "'RAW1-RAW4'"]
'TRF1-TRF25'
RF1-TRF25
'RAW1-RAW4'
AW1-RAW4

Answer 1

You're placing the flag in the wrong place. When you put re.I in the search method, you're inadvertently actually changing the start pos for the search . Take a look at re documentation for more on that. The re.I flag actually goes in the compile method. Also, you don't seem to need it as you use [A-Za-z] , which covers upper and lower case values, but in case you need it for more flags in the future, put it in the compile .

Your fixed code:

import re
def expandTrafficItemList(a):
    skip_list = []
    pat = re.compile(r'([A-Za-z]+)(\d+)-[A-Za-z]+(\d+)', flags=re.I)
    if a:
        c = a.split(',')
        print(c)
        for items in c:
            print(items)
            b = pat.search(items)
            print(b.group(0))

a = "'TRF1-TRF25','RAW1-RAW4'"
expandTrafficItemList(a)

output:

["'TRF1-TRF25'", "'RAW1-RAW4'"]
'TRF1-TRF25'
TRF1-TRF25
'RAW1-RAW4'
RAW1-RAW4