Findall function#

Function findall:

  • is used to search for all non-overlapping matches in string

  • returns:

    • list of strings that are described by regex if there are no groups in regex

    • list of strings that match with regex in the group if there is only one group in regex

    • list of tuples containing strings that matches with expression in the group if there are more than one group

Consider the work of findall with an example of ‘sh mac address-table output’:

In [2]: mac_address_table = open('CAM_table.txt').read()

In [3]: print(mac_address_table)
sw1#sh mac address-table
          Mac Address Table

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
 100    a1b2.ac10.7000    DYNAMIC     Gi0/1
 200    a0d4.cb20.7000    DYNAMIC     Gi0/2
 300    acb4.cd30.7000    DYNAMIC     Gi0/3
 100    a2bb.ec40.7000    DYNAMIC     Gi0/4
 500    aa4b.c550.7000    DYNAMIC     Gi0/5
 200    a1bb.1c60.7000    DYNAMIC     Gi0/6
 300    aa0b.cc70.7000    DYNAMIC     Gi0/7

The first example is a regex without groups. In this case findall returns a list of strings that matches with regex.

For example, with findall you can get a list of matching strings with vlan - mac interface and get rid of header in the output of command:

In [4]: re.findall(r'\d+ +\S+ +\w+ +\S+', mac_address_table)
['100    a1b2.ac10.7000    DYNAMIC     Gi0/1',
 '200    a0d4.cb20.7000    DYNAMIC     Gi0/2',
 '300    acb4.cd30.7000    DYNAMIC     Gi0/3',
 '100    a2bb.ec40.7000    DYNAMIC     Gi0/4',
 '500    aa4b.c550.7000    DYNAMIC     Gi0/5',
 '200    a1bb.1c60.7000    DYNAMIC     Gi0/6',
 '300    aa0b.cc70.7000    DYNAMIC     Gi0/7']

Note that findall returns a list of strings, not a Match object.

As soon as a group appears in regex, findall behaves differently. If one group is used in the expression, findall returns a list of strings that matches with expression in the group:

In [5]: re.findall(r'\d+ +(\S+) +\w+ +\S+', mac_address_table)

findall searches for a match of the entire string but returns a result similar to group method in Match object. If there are several groups, findall will return the list of tuples:

In [6]: re.findall(r'(\d+) +(\S+) +\w+ +(\S+)', mac_address_table)
[('100', 'a1b2.ac10.7000', 'Gi0/1'),
 ('200', 'a0d4.cb20.7000', 'Gi0/2'),
 ('300', 'acb4.cd30.7000', 'Gi0/3'),
 ('100', 'a2bb.ec40.7000', 'Gi0/4'),
 ('500', 'aa4b.c550.7000', 'Gi0/5'),
 ('200', 'a1bb.1c60.7000', 'Gi0/6'),
 ('300', 'aa0b.cc70.7000', 'Gi0/7')]

If such features of findall function prevent you from getting the needed result, it is better to use finditer function, but sometimes this behavior is appropriate and convenient to use.

An example of using findall in a log file parsing ( file):

import re

regex = (r'Host \S+ '
         r'in vlan (\d+) '
         r'is flapping between port '
         r'(\S+) and port (\S+)')

ports = set()

with open('log.txt') as f:
    result = re.findall(regex,
    for vlan, port1, port2 in result:

print('Loop between ports {} in VLAN {}'.format(', '.join(ports), vlan))

The result is:

$ python
Loop between ports Gi0/19, Gi0/16, Gi0/24 в VLAN 10