For loop#

A for loop is used in which the user wants to continuously repeat the execution of a given block of code or statements a known number of times. A for loop is used for iterating over a collection (that is either a list, a tuple, a dictionary, a set, or a string). For instance, a for loop in Python, is used to run over a specific number of times until a certain condition is reached.

ip_list = ["192.168.10.10", "192.168.10.11", "192.168.10.12"]

for ip in ip_list:
  print(ip)

192.168.10.10
192.168.10.11
192.168.10.12

range() Function#

The range() function returns a sequence of numbers, starting from 0 (default), increments by 1 (default), and stops before a specified number.

range(start, stop, step)

range(3, 6)


[3, 4, 5]
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

To loop through a specified number of times, the range() function returns a sequence of numbers, for loop is used to determine the number of iterations in advance.

for i in range(3):
    print(i)

0
1
2

The range() function defaults to 0 as a starting value, to specify the starting value by adding a parameter; range(2, 6), which means values from 2 to 6 (excluding 6).

for n in range (2,6):
    print ("VLAN " + str(n))

VLAN 2
VLAN 3
VLAN 4
VLAN 5

Break and Continue Statement#

With the break statement we can stop the loop before it has looped through all the items.

for i in range(10):
    print(i)
    if i == 5:
        break

0
1
2
3
4
5

Stop the loop when i == 5, but this time the break comes before the print.

for i in range(10):
    if i == 5:
        break
    print(i)

0
1
2
3
4

With the continue statement we can stop the current iteration of the loop, and continue with the next.

for i in range(5):
    if i == 2:  # 2 will skip in iteration
        continue
    print(i)

0
1
3
4

A nested loop is a loop inside a loop. The “inner loop” will be executed one time for each iteration of the “outer loop”.

ip_list = ['1.1.1.1', '2.2.2.2', '3.3.3.3']  # list
netmask = ("255.255.255.255",)  # tuple

for ip in ip_list:
    for mask in netmask:
        print(f'ip address {ip} {mask}')

ip address 1.1.1.1 255.255.255.255
ip address 2.2.2.2 255.255.255.255
ip address 3.3.3.3 255.255.255.255

For loop - network example#

In this code, you can iterate over a list of your device IP.

# IP list for network device
devices =['192.168.10.11', '192.168.10.12']

# For loop and list to connect multiple devices
for device in devices:
    print ('#### Connecting to the device ' + device + ' ####\n' )

#### Connecting to the device 192.168.10.11 ####

#### Connecting to the device 192.168.10.12 ####

For loop and range() function to create configuration template.

for num in range (0,2):
    print('int lo ' + str(num) + '\n')
    print(' ip address 1.1.1.' + str(num) + ' 255.255.255.255\n')

int lo 0
 ip address 1.1.1.0 255.255.255.255
int lo 1
 ip address 1.1.1.1 255.255.255.255

enumerate() Function#

when dealing with iterators(list/tuple) and want to keep a count of iterations. Python provid a built-in function enumerate() for this task. enumerate() method adds a counter to an iterable and returns two value tuple.

This enumerated object can then be used directly with for loops or converted into a list of tuples using the list() method.

  • Creating enumerate objects:

my_list = ["eat", "sleep", "go"]
my_tuple = enumerate(my_list)  

print(list(my_tuple))

[(0, 'eat'), (1, 'sleep'), (2, 'go')]

  • Creating enumerate object and printing out the tuple:

my_list = ["eat", "sleep", "go"]

for item in enumerate(my_list):
    print(item)

(0, 'eat')
(1, 'sleep')
(2, 'go')

The index value from which the counter is to be started, by default is 0.

  • Changing index value and printing out separately:

my_list = ["eat", "sleep", "go"]

for count, item in enumerate(my_list, 100):
    print (count, item)

100 eat
101 sleep
102 go

  • Getting desired output from tuple:

my_list = ["eat", "sleep", "go"]


for count, item in enumerate(my_list, 100):
    print(count)
    print(item)

100
eat
101
sleep
102
go