Extract string and assign to the variable using regex in Python

You can use regular expression to extract the value.

Try a pattern:

m = re.match("\W*RX packets[^:]*:(\d+)", line)

In a regular expression \d means a digit, and a + means one or more. You want to 'match' one or more numbers in the text. The brackets mean to capture what is found into a number, this number should be found after a specific text RX packets:.

You can find more details about regular expression in the official doc.

Your code would look like:

data= """
eth0      Link encap:Ethernet  HWaddr 08:ee:27:ff:b3:d7  
          inet addr:10.0.2.45  Bcast:10.3.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe00:b3d7/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:16178 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8559 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:14045795 (14.0 MB)  TX bytes:1355632 (1.3 MB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:666 errors:0 dropped:0 overruns:0 frame:0
          TX packets:666 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:72748 (72.7 KB)  TX bytes:72748 (72.7 KB)"""

import re

def findSeq(block,data):
    isInRightBlock= False
    for line in data.splitlines():
        if block in line:
            isInRightBlock= True
        m = re.match("\W*RX packets[^:]*:(\d+)", line)
        if m and isInRightBlock:
            isInRightBlock= False
            return m.group(1)


res= findSeq("eth0",data)
print res #Your Value

Output:

16178

Banchemark

from datetime import datetime
start_time_1 = datetime.now()
res= findSeq("eth0",data)
print('Duration: {}'.format(datetime.now() - start_time_1))

from datetime import datetime
start_time_2 = datetime.now()
re.search(r'eth0.*?RX packets:(\d+)',data,re.DOTALL).group(1)
print('Duration: {}'.format(datetime.now() - start_time_2))

Output:

Duration: 0:00:00.000547
Duration: 0:00:00.000344

NT: You can optimize the way it checks the right block.