Python正则表达式字母数字字符串，其数字部分介于两个值之间

Question

I am terrible at regex in general, but I would be interested to know if there is a method to check if the numeric part of an alpha-numeric string is between two values, or less/greater than a certain value?

For example if I have a string to search in a file which has multiple numeric variations like below:

key_string (870 bytes)
key_string (1500 bytes)
key_string (70 bytes)

Is it possible to extract the 'key_string' string only on whether the '(xxxx bytes)' part is between a certain threshold, or less/greater than a certain value?

For example if I want to find all the above 'key_string' example where the second part is below 1200 bytes, can I print out:

key_string (870 bytes)
key_string (70 bytes)

and ignore the string below in one regular expression? :

key_string (1500 bytes)

Answer 1

You can use re.findall() to search along with regex.

Explanation of regex as below:

key_string\s+\((\d+)\s+bytes\)

Debuggex Demo

Code:

import re

with open('result.txt') as fh:
    for l in fh:
        a = re.findall(r"key_string\s+\((\d+)\s+bytes\)",l.strip())
        if len(a) > 0 and int(a[0]) < 1200:
            print (l)

Output:

C:\Users\dinesh_pundkar\Desktop>python c.py
key_string (870 bytes)

key_string (70 bytes)

C:\Users\dinesh_pundkar\Desktop>

Code 2 as suggested by @WiktorStribiżew :

import re

pattern = r'key_string\s+\((\d+)\s+bytes\)'
regex = re.compile(pattern, re.IGNORECASE)
with open('result.txt') as fh:
    for match in regex.finditer(fh.read()):
        if int(match.group(1)) < 1200:
            print((match.group()))