III-Networking
introduces
Python Basics for Network
Engineers
By: Sajjad Ghaffoori
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- Python Programming Language
- A scripted language
- source-free
- object-oriented
- simple understandable text
- standard-library
- indentation sensitive
- tabs or spaces (4)
- can integrate with other encoding languages
- use python interpreter for a quick interface to python processing
- use python editor to code programs to run by python
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- Python Virtual Environments
- A separate directory structure
- with a different python version
- and packages and modules
- independent from the base version
- if a developed application is familiar with/based on
- a specific version of python
- and if upgrading python in the future might
- add a risk to break the functions/code of the application
- using virtual environments will lock components and modules
- of an application, into a single package
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- Python Comments
- insert a note to yourself or other programmers
- to highlight a comment about the code
- comments can start with a hash symbol #
- this will only allow one line for a comment
- no new line for the same comment
- or use the triple quotes ‘’’ ‘’’ enclosing a string
- this allows for multiple lines per comment
- a carriage return won’t break the comment sequence
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- Python Variables
- A label, maps to a stored object
- ask python to process/print the variable label only
- python will take care of the value of that variable
- variable name rules
- must start with an alphabetic letter, or underscore
- but not a number
- case sensitive
- in total, it can contain, letter, numbers, and underscore only
*the object assigned to a variable can be a variety of data types
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- Python Data Types
- Integers & Floating Points
- An integer is a whole number without a decimal points (10)
- a floating points is a number with a decimal points or exponents
- 10e5 = 100,000 , or 10.5
- Python’s Numeric Operations
+
sum
10+6 = 16
-
subtract
10-6 = 4
*
multiply
10*6 = 60
/
divide
10/6 = 1.6666666666666667
//
divide/no remainder
10//6 = 1
%
modulus division
10%6 = 4
**
exponent
10*6 = 1,000,000
*order of the process is: parentheses --- power --- multiply. --- division --- addition --- subtraction --- L->R
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- Python Data Types
- Booleans
- A Boolean object can have a value of 2 only
- True or False
- comparison operators evaluates between 2 Boolean objects
- Boolean comparison operators can be
<
less than
6 < 10
TRUE
>
greater than
6 < 10
FALSE
<=
less than or equal
6 <= -10 FALSE
>=
greater than or equal
6 >= -10 TRUE
==
equal to
6 == 10
FALSE
!=
not equal to
6 != 10
TRUE
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- Python Data Types
- Strings
- a set of characters, stored from left to right
- enclosed by a double quote (“”)
- the string “10” is only a string of 2 characters
- and not considered as an integer to be numerically processed
- using the integer function int()
- a string can be dealt with as an integer
>>> int(’10’) + 6 = 16
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- Python Data Types
- String index
- the location of a character, counted starting from the left side and from the value of “0”
- the 0 index of the string “Hello” is the “H” character
>>> v = “Hello”
>>> v [0] = “H”
>>> v [0:2] = “He”
>>> v [0:5] = “Hello”
>>> v [:2] = “He”
>>> v [2:] = “llo”
>>> v [-2:] = “lo”
>>> v [:-2] = “Hel”
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- Python Data Types
- String operations
- operations with string can deal with the characters in a simple manner without modifying them
- “Hello” + “III” = “Hello III”
- “Hello” * 3 =“Hello Hello Hello”
- String Methods
str.capitalize()
Capitalize the string
str.center(width[, fillchar])
Center justify the string
str.endwith(suffix[, start[, end]])
Add an ending string to the string
str.find(sub[, start[, end]])
Find the index position of the characters in a string
str.lstrip([chars])
Remove whitespace characters from the end of the string
str.replace(old, new[, count])
Replace characters in the string
str.lower()
Make the string all lowercase
str.rstrip([chars])
Strip whitespace characters from the front of the string
str.strip([chars])
Remove whitespace characters from the beginning and end of the string
str.upper()
Make the string all uppercase
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- Python Data Types
- Lists
- A collection of values stored in one variable
- collage the values inside a square bracket []
- separate the values using a comma ,
- Certs = [ “CCNA” , “CCNP” , “CCIE” ]
- values in a list can be a variety of python data types
*lists can be empty, *python supports a built-in list() function
- Lists Index
- each value inside the square brackets has an index, starting from “0”
- Certs[2] = “CCIE”
- List Cat with + operator
- Certs1 = [ “CCNA” , “CCNP” , “CCIE” ] , Certs2 = [ “JNCIA” , “JNCIP” , “JNCIE” ]
- Certs3 = Certs1 + Certs2 == [ “CCNA” , “CCNP” , “CCIE” , “JNCIA” , “JNCIP” , “JNCIE” ]
*same string operations applies to lists operations
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- Python Data Types
- Tuples
- an immutable lists
- where lists are mutable (modifiable) used for non-constant values
- tuples are immutable (non-modifiable) used for constant values
- Certs = ( 2024 , “ENCOR” , “ENAUTO” )
- support the type() function to declare the tuple class
- same operations of lists apply
- modifying operations won’t work
- try Certs[1] =“NOT-UPDATED” in both lists and tuples
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- Python Data Types
- Dictionaries
- also, a collection of values
- the collection has no index method
- built using key:value pairs
- keys are immutable: integers, strings, floats, Booleans)
- values are all the python data types including lists and tuples
- Dictionaries themselves are mutable
- they enclose the collection of data using curly braces { }
- and separate each key:value pair using a comma ,
- CompanyInfo = { “Name”:”III” , “Type”:”LLC” , “Age”:2 , “Certs”(“Cisco” , “Juniper” , “AWS”) }
- type(CompanyInfo) == <class ‘dict’>
- to investigate the values, refer to keys instead of index
- CompanyInfo[“Type”] == “LLC”
- adding a new pair can be done just by typing the new values >>> CompanyInfo[“Domain”] = “IT”
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- Python Data Types
- Sets
- as dictionaries, sets uses curly braces, and it is mutable
- a set is just an unordered grouping of data
- frozen sets are immutable sets
>>> values1 = {1, 2, 4, 6, 8, 10, 12}
>>> values2 = {1, 3, 5, 7, 9}
>>> type(values)
<class ‘set’>
- join 2 sets with no duplicates
>>> values1 | values
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
- intersect 2 sets showing only the duplicates
>>> values1 & values2
{1}
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- Python Input & Output Function
- The input() function
- python will prompt a message asking for an input
- from the client or the user of the program
- any input (response) from the user, is considered a string (only)
>>> Username = input (“Type Username: “)
Type Username: III-Networking
>>> Username
“III-Networking”
- in cases where the input is designed to not be a string (default)
- an additional converting function would be needed
>>> Temperature = integer (input (“What is the Temp Today?: “))
What is the Temp Today?: 25
>>> Temperature
25
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- Python Input & Output Function
- The output function
- Named as the Print() Function
- prints the output of a code or a program
>>> print(“Hello III”)
Hello III
- each line processed in the print() function end with a \n character
- which represents the function of “new line”
>>> print(“Hello\nIII”)
Hello
III
- text control codes
\\: Backslash
\b: Backspace
\t: Tab
\r: Carriage Return
\’: Single Quote
\”: Double Quote
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- Python Input & Output Function
- The open() function
- opens and reads a file content, line by line
- the open() function should contain the file name inside the paratheses ()
- and the entire object can be stored in a variable
- an open mode can be specified as well, to determine what should the function do
- to the content in the file
- open() functions should be closed with a close() function
readdata = open(“textfile.txt”, “r”)
print(readdata.read())
readdata.close()
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- Python Input & Output Function
- The open() function
- The with statement
- uses the open() function, without requiring a close() function
with open("textfile.txt", "r") as data:
print(data.read())
- The append “a+” statement
- to append, write data to a file
with open("textfile.txt", "a+") as data:
data.write('\nFourth line added by Python’)
with open ("textfile.txt", "r") as data:
print(data.read())
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- Python Input & Output Function
- The open() function
- modes can be
r: Open for reading (default)
w: Open for writing, truncating the file first
x: Open for exclusive creation, failing if the file already exists
a: Open for writing, appending to the end of the file if it exists
b: Open in binary mode
t: Open in text mode (default)
+: Open for updating (reading and writing)
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- Python Conditionals
- If statements
- evaluates elements and determines its truth
- if statements is a Boolean logic
- a program can start with an “if” statement
- have many “elif” else-if statements
- and closed with an “else” statement
- all of the 3 above conditions are optional, per-program
>>> n = 20
>>> if n == 20:
...
print('The number is 20’)
...
The number is 20
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- Python Conditionals
- Else-if statement
- Else statement
>>> n = 3
score = int(input('What was your test score?:’))
>>> if n == 17:
if score >= 90:
...
print('Number is 17’)
... elif n < 10:
...
print('Number is less than 10’)
... elif n > 10:
...
print('Number is greater than 10’)
...
Number is less than 10
print('Grade is A’)
elif score >= 80:
print('Grade is B’)
elif score >= 70:
print('Grade is C’)
elif score >= 60:
print('Grade is D’)
else:
print('Grade is F’)
What was your test score?:53
Grade is F
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- Python Looping
- repetitive operation per condition
- For Loops
- repeats or continue to iterate based on a specific number of times
>>> numbers=(1,2,3,4,5)
>>> for variable in numbers:
...
print(variable)
...
1
2
3
4
5
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- Python Looping
- For Loops
- the range() function can cooperate with the for loop
- to further customize the looping range or period
- from which value to start and to which value to stop
- as well as the increment value
>>> for x in range(3):
>>> for x in range(1,3):
>>> for x in range(1,11,3):
...
...
...
print(x)
print(x)
...
...
...
0
1
1
1
2
4
2
print(x)
7
10
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- Python Looping
- While Loop
- evaluates and iterates as long as the condition is “TRUE”
- can continue to iterate forever
- can cooperate with the “else” statement
>>> count = 1
>>> while (count < 5):
...
print("Loop count is:", count)
...
count = count + 1
... else:
...
print("loop is finished")
...
Loop count is: 1
Loop count is: 2
Loop count is: 3
Loop count is: 4
loop is finished
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- Python Looping
- While Loop
- to exit the infinite while loop
- a break statement can be involved in the program
while True:
string = input('Enter some text to print. \nType "done" to quit> ‘)
if string == 'done’ :
break
print(string)
print('Done!’)
Enter some text to print.
Type "done" to quit> Good luck on the test!
Good luck on the test!
Enter some text to print
Type "done" to quit> done
Done!
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- Python Functions
- A function in python can take inputs, process, and return outputs
- represents the key concept of DRY
- Don’t Repeat Yourself
- meaning, define a function at the beginning
- refer to it multiple times, in different ways, throughout the code
- Functions Types
- built-in python: the print() function
- custom created functions
- Functions format
- def functionname():
- can’t start with a number
>>> def devnet():
'''prints simple function'‘’
print('Simple function')
>>> devnet()
Simple function
*try help(devnet)
- can’t reuse a default standard function name
- accepts combinations of letters, numbers, and special characters
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- Python Functions
- Positional Arguments
- arguments allows to store multiple values in a function
- the function will later summon a value or more per the code request
- making the function usable for multi-purpose, multi-output
- try the max() function and see the output
>>> max(40, 30, 20, 10)
40
- Parameters
- allows to pass data to a function
- parameters are variables
>>> def sub(arg1, arg2):
result = arg1 - arg2
return result
>>> sub(30, 15)
15
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- Python Functions
- Keyword Arguments
- pass key:value pairs to a function
- positional argument (*args) vs. keyword arguments (**kwargs)
(**args)
(*args)
>>> def hello(*args):
for arg in args:
print("Hello", arg, "!")
>>> hello(‘Mohammed’ , ‘Ali’)
Hello Mohammed !
Hello Ali !
>>> def hello(**kwargs):
for key, value in kwargs.items():
print("Hello", value, "!")
>>> hello(kwarg1=‘Mohammed', kwarg2=‘Ali')
Hello Mohammed !
Hello Ali !
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- Python Classes
- A Class structures data to describe information about an object
- data can be a variety of information for one object
- the first default data should be “self”
class Router:
'''Router Class'‘’
def __init__(self, model, swversion, ip_add):
'''initialize values'‘’
self.model = model
self.swversion = swversion
self.ip_add = ip_add
rtr1 = Router(‘C8Kv', ‘17.2.1', ‘100.64.10.1’)
- test the above program by asking for a specific information
>>> rtr1.model
“C8Kv”
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- Python Classes
- new information/data can be inserted to an object at any time
>>> rtr1.desc = 'virtual router’
>>> rtr1.desc
'virtual router’
- adding a new object (variable) to program doesn’t require to built a new class (DRY)
>>> rtr2= Router('isr4221', '16.9.5', '10.10.10.5‘)
>>> rtr2.model
'isr4221‘
*the __ double Under score is called a method
*try the function getdesc() with methods and classes
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- Python Classes
class Router:
'''Router Class'‘’
def __init__(self, model, swversion, ip_add):
‘''initialize values'‘’
self.model = model
self.swversion = swversion
self.ip_add = ip_add
def getdesc(self):
‘''return a formatted description of the router'‘’
desc = f'Router Model
:{self.model}\n’\
f'Software Version
:{self.swversion}\n’\
f'Router Management Address
:{self.ip_add}’
return desc
rtr1 = Router('iosV', '15.6.7', '10.10.10.1')
rtr2 = Router('isr4221', '16.9.5', '10.10.10.5')
print('Rtr1\n', rtr1.getdesc(), '\n', sep='')
print('Rtr2\n', rtr2.getdesc(), sep='')
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- Python Classes
- classes supports inheritance, to reuse a class for another object
- without redefining the class structure again (DRY)
class Router:
'''Router Class'‘’
def __init__(self, model, swversion, ip_add):
'''initialize values'‘’
self.model = model
self.swversion = swversion
self.ip_add = ip_add
def getdesc(self):
'''return a formatted description of the router'‘’
desc = (f'Router Model
:{self.model}\n’
f'Software Version
:{self.swversion}\n’
f'Router Management Address:
{self.ip_add}’)
return desc
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- Python Classes
class Switch(Router):
def getdesc(self):
'''return a formatted description of the switch'‘’
desc = (f'Switch Model
:{self.model}\n’
f'Software Version
:{self.swversion}\n’
f'Switch Management Address
:{self.ip_add}’)
return desc
rtr1 = Router('iosV', '15.6.7', '10.10.10.1’)
rtr2 = Router('isr4221', '16.9.5', '10.10.10.5’)
sw1 = Switch('Cat9300', '16.9.5', '10.10.10.8’)
print('Rtr1\n', rtr1.getdesc(), '\n', sep=‘’)
print('Rtr2\n', rtr2.getdesc(), '\n', sep=‘’)
print('Sw1\n', sw1.getdesc(), '\n', sep='')
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- Python Modules
- Modular, as English states! ☺
- modules are a groupings of python’s classes and functions
- with a common use for a program
- thousands of libraries are standard python libraries
- many comes in the Python Standard Library upon installation
- others should be manually downloaded using the “pip” command
- thousands more are 3rd party libraries
- reviewing a library
- use the “import” command to summon a library with its functions and classes
>>> import libraryname
>>> dir (libraryname)
>>> help (libraryname)
>>> help (libraryname.functionname)
*throughout the code, a library name can be shorted using the “as” (import library as lib)
*importing a function from a library is possible, (from library import function1)
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- Python Modules for Cisco Infra.
- xmltodict: translates between XML-formatted files and python dictionaries
- json: translates between JSON-formatted files and python dictionaries
- PyYAML: translates between YAML formatted files and python dictionaries/lists
- pyang: a utility to verify YANG Modules
- requests: to interact with REST APIs and HTTP requests
- ncclient: to integrate with NETCONF
- netmiko: to initiate SSH connection to clients
- pysnmp: to interact with SNMP NMS, without APIs
- napalm: to function in a multivendor environments
- nornir: multithreaded framework with inventory management to work with large numbers of net devices
- unittest: to test the functionality of a python code
- pyats: to validate python codes for Cisco products (IaC)
- csv: to deal with excel spreadsheets as a data source imported in a python code
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- Python Codes for Cisco
- refer to some python codes written to work on Cisco devices
- pythonex_ssh_ciscoRouter_iosXE_SHOW
- pythonex_ssh_ciscoRouter_iosXE_CONFIG
- pythonex_ssh_multiciscoRouter_iosXE_SHOW
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