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Python for Network Engineers Week 1

In this post, I am recording my learnings from the Python for Network Engineers course taught by Kirk Byers.

https://pynet.twb-tech.com/free-python-course.html

It’s a free ten-week, email-course for network engineers wanting to learn Python.

Create a Virtual Environment

Create a virtual environment in the current directory with the python3 -m venv <name>. In this case, I am creating a venv named Python4Networking. Once it is created, you need to activate the venv with the source <name>/bin/activate.

Then the prompt changes showing the venv name. In this case (Python4Networking) (base).

Last login: Mon Jul 22 16:31:14 on console

(base) pradeep:~$
(base) pradeep:~$cd LearnPython 
(base) pradeep:~$which python
/Users/pradeep/opt/anaconda3/bin/python
(base) pradeep:~$which python3
/Users/pradeep/opt/anaconda3/bin/python3
(base) pradeep:~$python3 -m venv Python4Networking
(base) pradeep:~$source Python4Networking/bin/activate
(Python4Networking) (base) pradeep:~$pwd
/Users/pradeep/LearnPython
(Python4Networking) (base) pradeep:~$

Input and Output

Next, lets read from standard input using the input method and print to the standard output using the print.

For print, there are a couple of methods. Three different methods are shown here. Using %, .format and f string methods.

(Python4Networking) (base) pradeep:~$python3
Python 3.9.12 (main, Apr  5 2022, 01:53:17) 
[Clang 12.0.0 ] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> my_ip = input ("Enter an IP address: ")
Enter an IP address: 192.168.100.1
>>> my_ip
'192.168.100.1'
>>> print(my_ip)
192.168.100.1
>>> print ("My IP address is : %s" % my_ip)
My IP address is : 192.168.100.1
>>> print ("My IP address is {}".format(my_ip))
My IP address is 192.168.100.1
>>> print (f"My IP address is {my_ip}")
My IP address is 192.168.100.1
>>>

When there are multiple variables,

>>> ip1 = "192.168.1.1"
>>> ip2 = "192.168.1.2"
>>> print (f"My two IPs are {ip1}, {ip2}")
My two IPs are 192.168.1.1, 192.168.1.2
>>>

Using the .format method

>>> print ("My two IPs are {}, {}".format(ip1,ip2))
My two IPs are 192.168.1.1, 192.168.1.2
>>>

Using the % method

>>> print ("My two IPs are %s %s" % (ip1,ip2))
My two IPs are 192.168.1.1 192.168.1.2
>>>

Of all three methods, format strings f is recommended.

Dir and Help

>>> type(ip1)
<class 'str'>
>>> dir(ip1)
['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'removeprefix', 'removesuffix', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
>>> help(ip1.split)

>>> 

Help on built-in function split:

split(sep=None, maxsplit=-1) method of builtins.str instance
    Return a list of the words in the string, using sep as the delimiter string.
    
    sep
      The delimiter according which to split the string.
      None (the default value) means split according to any whitespace,
      and discard empty strings from the result.
    maxsplit
      Maximum number of splits to do.
      -1 (the default value) means no limit.

Strings and Formatting

Let’s see split in action

>>> ip1.split
<built-in method split of str object at 0x7fd4035398b0>
>>> ip1.split()
['192.168.1.1']
>>> ip1.split(".")
['192', '168', '1', '1']
>>> 

>>> ip1 = "192.168.1.1"
>>> type(ip1)
<class 'str'>
>>> ip1=ip1.split(".")
>>> type(ip1)
<class 'list'>
>>> ip1
['192', '168', '1', '1']
>>>

Original value is unmodified. You can use the same name to reassign. In this case we have changed from str to list with the split method.

Let’s see the opposite of split that is join.

>>> mac1 = ["01","02","03","04","05","06"]
>>> type(mac1)
<class 'list'>
>>> (":").join(mac1)
'01:02:03:04:05:06'
>>> ("-").join(mac1)
'01-02-03-04-05-06'
>>> 
>>> mac1=("-").join(mac1)
>>> type(mac1)
<class 'str'>
>>> mac1
'01-02-03-04-05-06'
>>>

In this case, we converted from list to str.

Now, let’s format the output a bit, left aligned (default), right aligned, and center aligned. You can use it with strings, expressions, and variables.

>>> print(f"{mac1:20}")
01-02-03-04-05-06   
>>> print(f"{mac1:>20}")
   01-02-03-04-05-06
>>> print(f"{mac1:^20}")
 01-02-03-04-05-06  
>>> 

>>> print(f"{'MAC Address':^20}")
    MAC Address     
>>> print(f"{'-' * 20:^20}")
--------------------
>>> print(f"{mac1:^20}")
 01-02-03-04-05-06  
>>> 

>>> print (f"My IP and MAC are {ip2}, {mac1}")
My IP and MAC are 192.168.1.2, 01-02-03-04-05-06
>>> print (f"My  IP and MAC are {ip2:^30}, {mac1:^30}")
My  IP and MAC are          192.168.1.2          ,       01-02-03-04-05-06       
>>> print (f"My  IP and MAC are {ip2:^20}, {mac1:^20}")
My  IP and MAC are     192.168.1.2     ,  01-02-03-04-05-06  
>>>
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