Python’s standard library is very extensive, offering a wide range of facilities. The library contains built-in modules (written in C) that provide access to system functionality such as file I/O that would otherwise be inaccessible to Python programmers, as well as modules written in Python that provide standardized solutions for many problems that occur in everyday programming

In this tutorial, we will learn everything which a beginner and a DevOps engineer should know in Python. We will cover the basic definition of python and some brilliant examples which will be enough to get you started with Python and for sure you will love it.

Table of content

1. What is Python?
2. Prerequisites
3. Python Keywords
   • Python Numbers
   • Python Strings
   • Python Tuple
   • Python Lists
   • Python Dictionary
   • Python Sets
4. Python variables
5. Python Built-in functions
6. Python Handling Exceptions
7. Python Functions
8. Python Searching
9. Conclusion

What is Python?

Python is a high-level, oops-based, interactive, and general-purpose scripting programing language. Python is a language that is used as a backend as well as a frontend language. It focuses on objects over functions.

Python is also an interpreted language because it converts codes into machine-level code even before it runs. It works on a variety of protocols such as HTTPS, FTP , SMTP, and many more. The latest version is 3.9.2 which was released in December 2020. Python works very well with most of the such as atom, notepad ++, vim.

Python works on windows, Linux, and macOS systems, and many more. For Windows OS it can run a single command on windows terminal and for Linux & macOS it can easily run on the shell without needing to save the program every time.

Prerequisites

• Python doesn’t come installed on windows so make sure you have Python installed on windows machine. To see how to install python on windows click here.
• For macOS and Linux Python comes installed by default but could be the older version such as python2. To check python version run the command.

• In case if your system has Python2 or if you receive an error message “Python not found” then you need to run the following command to install python on macOS or Linux.

sudo apt install python3

Python Keywords

Python reserves certain words for special purposes known as keywords such as

• continue
• def
• del
• break
• class
• if
• return

Python Data types

Whatever program you write in Python is data and this data contains some values which are also known as objects. Each object has a type known as data types. These data types are either mutable in nature that is modifiable or immutable in nature that is unmodifiable.

Python contains numerous built-in data types such as:

Python Numbers

Numbers are either integers or floating-point.

• Decimal integer: 1 , 2
• Binary integer: 0b010101
• Octal integer: 0o1
• Hexadecimal integer: 0x1
• Floating point: 0.0 , 2.e0

Boolean

Booleans are represented by either True or False

Python String

Python strings are a collection of characters surrounded by quotes ” “. There are different ways in which strings are declared such as:

1. str() – In this method you decalre the characters or words or data inside the double quotes.

2. Directly calling it in quotes – “Hello, this is method2 to display string”

3. Using Format – format method was introduced in Python3 and uses curly brackets {} to replace the values.
   • In below example you will notice that first curly bracket will be replaced by first value a and second will be replaced by b
   • If you provide any numerical value inside the curly braces it considers it as index and then retrieve from the given values accordingly as shown in the second example below.
   • if you provide key value pair then values are substituted according to key as shown in the third example below.

'{} {}'.format('a','b')

'{0} {0}'.format('a','b')

'{a} {b}'.format(a='apple', b='ball')

4. Using f string – f string are prepended with either f or F before the first quotation mark. The value is subsituted with the variables declared.

a=1 # Declaring a 
f"a is {a}" 

5. Template strings – Template strings are designed to offer a simple string substitution mechanism. These built-in methods work for tasks where simple word substitutions are necessary.

from string import Template
new_value = Template("$a b c d")       #  a will be substituted here
x = new_value.substitute(a = "Automation")
y = new_value.substitute(a = "Automate")
print(x,y)

Some Tricky Examples of declaring string

Input String

print('This is my string 1')   # Correct String
print("This is my string 2")   # Correct String
# print('This is not a string ") # InCorrect String as you cannot used mixed quotes
# print("This is not a string')  # InCorrect String as you cannot used mixed quotes

# Examples of Special characters inside the String such as quotes

# print('Hello's Everyone')  # Incorrect Statement
print('Hello\'s Everyone')   # Correct Statement after using escape (To insert characters that are illegal in a string, use an escape character. )
print("Hello's Everyone")    # Correct Statement enclose within double quotes
print('Hello "shanky')       # COrrect STatement 
print('Hello "shanky"')      # Correct STatment
# print("Hello "S"shanky") # Incorrect Statement
print("Hello ""shanky")  

# No need to Escape if using triple quotes but proper use of triple quotes
print(''''This is not a string "''')
print('''Hello" how' are"" u " I am " f'ine'r''')
print('''''Hello" how' are"" u " I am " f'ine'r''')
print("""'''''Hello" how' are"" u " I am " f'ine'r""") 

Output String

This is my string 1
This is my string 2
Hello's Everyone
Hello's Everyone
Hello "shanky
Hello "shanky"
Hello shanky
'This is not a string "
Hello" how' are"" u " I am " f'ine'r
''Hello" how' are"" u " I am " f'ine'r
'''''Hello" how' are"" u " I am " f'ine'r

Python Tuple

Tuples: Tuples are immutable ordered sequence of items that cannot be modified. The items of a tuple are arbitrary objects and may be of different types and allow duplicate values. For Example

# 10,20,30,30 are fixed at respective index 0,1,2,3 positions 
(10,20,30,30) or (3.14,5.14,6.14)

Python Lists

Lists: The list is a mutable ordered sequence of items. The items of a list are arbitrary objects and may be of different types. List items are ordered, changeable, and allow duplicate values.

[2,3,"automate","2"]

Python Dictionaries

Dictionary are written as key:value pair , where key is an expression giving the item’s key and value is an expression giving the item’s value. A dictionary is a collection which is ordered*, changeable and does not allow duplicates.

# Dictionary with three items where x,y and z are keys.
# where x,y and z have 42, 3.14 and 7 as the values.
{'x':42, 'y':3.14, 'z':7} 

Python Sets

Sets: Set stores multiple items in a single variable. It contains unordered and unindexed data. Sets cannot have two items with the same value.

{"apple", "banana", "cherry"}

Python variables

Variables are stored as a information it could be number , symbol , name etc. which are used to be referenced. Lets see some of the examples of Python variables.

• There are few points one must remember when using variables such as
  • Variables cannot start with digits
  • Spaces are not allowed in variables.
  • Avoid using Python keywords

Example 1:

• In below example var is a variable and value of var is this is a variable

var="this is a variable" # Defining the variable
print(var)    # Printing the value of variable

Example 2:

• In below example we are declaring three variable.
  • first_word and second_word are storing the values
  • add_words is substituting the variables with values

first_word="hello"
second_word="devops"
add_words=f"{first_word}{second_word}"
print(add_words)

• If you wish to print words in different line then use "\n" as below

first_word="hello"
second_word="devops"
add_words=f"{first_word}\n{second_word}"
print(add_words)

Dictionary

In simple words these are key value pairs where keys can be number, string or custom object. Dictionary are represented in key value pairs separated by comma within curly braces.

map = {'key-1': 'value-1', 'key-2': 'value-2'}

• You can access the particular key using following way

map['key-1']

Lets see an example to access values using get() method

my_dictionary = {'key-1': 'value-1', 'key-2': 'value-2'}
my_dictionary.get('key-1')    # It will print value of key-1 which is value-1
print(my_dictionary.values()) # It will print values of each key
print(my_dictionary.keys())   # It will print keys of each value
my_dictionary.get('key-3')    # It will not print anything as key-3 is missing

Lists

Lists are ordered collection of items. Lists are represented using square brackets containing ordered list of item.

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] # Example of List

• We can add or remove items from the list using built in function such as pop() or insert() or append() and many more. Lets us see an example.

The contents of one list can be added to another using the extend method:

list1 =['a', 'b', 'c', 'd']
print(list1)                        # Printing only List 1
list2 = ['e', 'f']
list2.extend(list1)
print(list2)                        # Printing List 2 and also 1

• Use insert() to add one new guest to the beginning of your list.
• Use insert() to add one new guest to the middle of your list.
• Use append() to add one new guest to the end of your list.

Python Built-in functions

There are various single line command which are already embedded in python library and those are known as built in functions. You invoke a function by typing the function name, followed by parentheses.

• To check the Python version on windows or Linux machine run the following command.

python3 --version

• To print the output of a program , use the print command.

print("Hello Devops")

• To generate a list of number through a range built-in function run the following command.

list(range(0,10))

Handling Exceptions

Exceptions are error which causes a program to stop if not handled properly. There are many built-in exceptions, such as IOError, KeyError, and ImportError. Lets see a simple example below.

• Here we defined a list of characters and stored it in a variable devops
• Now, while true indicated that till the ,condition is true it will execute the try block.
• .pop() is built in method to remove each item one by one.
• Now in our case as soon as all the characters are removed then except block catches the IndexError and prints the message.

devops = ['d','e','v','o','p','s']
 
while True:
    try:
        devop = devops.pop()
        print(devop)
    except IndexError as e:
        print("I think I did lot of pop ")
        print(e)
        break
 
Output:
 
s
p
o
v
e
d
I think I did lot of pop
pop from empty list

Python Functions

Earlier in this tutorial we have already seen that there are numerous built in function and some of them you used above. But you can define and create your own functions. Lets see the syntax of function.

def <FUNCTION NAME>(<PARAMETERS>):
    <CODE BLOCK>
<FUNCTION NAME>(<ARGUMENTS>)

Lets look at some of the Python functions examples

EXAMPLE 1

• Here each argument use order of arguments to assign value which is also known as positional argument.
• a and b variables are parameters which are required to run the function
• 1 and 2 are arguments which are used to pass the value to the function ( arguments are piece of information that’s passed from a function call to a function)

def my_function(a,b):
  print(f" value of a is {a}")
  print(f" value of b is {b}")
my_function(1, 2)

EXAMPLE 2:

• With keyword arguments, assign each argument a default value:

def my_function(a=3,b=4):
  print(f" value of a is {a}")
  print(f" value of b is {b}")
my_function()

EXAMPLE 3

Passing arbitrary number of arguments. When you are not sure about the number of parameters to be passed then we call it as arbitrary. Lets look at an example

• Find the Even in the string

mylist = []
def myfunc(*args):      #  args is to take any number of arguments together in myfunc
    for item in args:
        if int(item)%2 == 0:
            mylist.append(item)
    print(mylist)
myfunc(5,6,7,8,9)

EXAMPLE 4

• IF LOOP: Find the least among two numbers if both numbers are even else return greater among both the numbers

def two_of_less(a,b):    # Defining the Function where a and b variables are parameters
    if a%2==0 and b%2==0:
      print(min(a,b))       # using built in function min()
    if a%2==1 or b%2==1:
      print(max(a,b))       # using built in function max()
two_of_less(2,4)

EXAMPLE 5

• Write a function takes a two-word string and returns True if both words begin with same letter

def check(a):
    m = a.split()
    if m[0][0] == m[1][0] :
     print("Both the Words in the string starts with same letter")
    else:
     print("Both the Words in the string don't start with same letter")    
check('devops Engineer')

Python Searching

The need to match patterns in strings comes up again and again. You could be looking for an identifier in a log file or checking user input for keywords or a myriad of other cases.

Regular expressions use a string of characters to define search patterns. The Python re package offers regular expression operations similar to those found in Perl.

Lets look at example which will give you overall picture of in built functions which we can use with re module.

• You can use the re.search function, which returns a re.Match object only if there is a match.

import re
import datetime
 
name_list = '''Ezra Sharma <esharma@automateinfra.com>,
   ...: Rostam Bat   <rostam@automateinfra.com>,
   ...: Chris Taylor <ctaylor@automateinfra.com,
   ...: Bobbi Baio <bbaio@automateinfra.com'''
 
# Some commonly used ones are \w, which is equivalent to [a-zA-Z0-9_] and \d, which is equivalent to [0-9]. 
# You can use the + modifier to match for multiple characters:
 
print(re.search(r'Rostam', name_list))
print(re.search('[RB]obb[yi]',  name_list))
print(re.search(r'Chr[a-z][a-z]', name_list))
print(re.search(r'[A-Za-z]+', name_list))
print(re.search(r'[A-Za-z]{5}', name_list))
print(re.search(r'[A-Za-z]{7}', name_list))
print(re.search(r'[A-Za-z]+@[a-z]+\.[a-z]+', name_list))
print(re.search(r'\w+', name_list))
print(re.search(r'\w+\@\w+\.\w+', name_list))
print(re.search(r'(\w+)\@(\w+)\.(\w+)', name_list))
 

OUTPUT

<re.Match object; span=(49, 55), match='Rostam'>
<re.Match object; span=(147, 152), match='Bobbi'>
<re.Match object; span=(98, 103), match='Chris'>
<re.Match object; span=(0, 4), match='Ezra'>
<re.Match object; span=(5, 10), match='Sharm'>
<re.Match object; span=(13, 20), match='esharma'>
<re.Match object; span=(13, 38), match='esharma@automateinfra.com'>
<re.Match object; span=(0, 4), match='Ezra'>
<re.Match object; span=(13, 38), match='esharma@automateinfra.com'>
<re.Match object; span=(13, 38), match='esharma@automateinfra.com'>

1. Understanding the difference between high level and low level language.
2. Interpreted v/s Compiled Language
3. Introduction to Python
4. How Python Works ?
5. Python Interpreter
6. Python Standard Library
7. Python Implementations
8. Python Installation
   • Python Installation on Linux Machine
   • Python Installation on Windows Machine
   • Python Installation on MacOS
9. Conclusion

Understanding the difference between High & Low-level Languages

High-Level Language: High-level language is easier to understand than is it is human readable. It is either compiled or interpreted. It consumes way more memory and is slow in execution. It is portable. It requires a compiler or interpreter for a translation.

Low-Level Language: Low-level Languages are machine-friendly that is machines can read the code but not humans. It consumes less memory and is fast to execute. It cannot be ported. It requires an assembler for translation.

Interpreted v/s Compiled Language

Compiled Language: Compiled language is first compiled and then expressed in the instruction of the target machine that is machine code. For example – C, C++, C# , COBOL

Interpreted Language: An interpreter is a computer program that directly executes instructions written in a programming or scripting language, without requiring them previously to have been compiled into a machine language program and these kinds of languages are known as interpreter languages. For example JavaScript, Perl, Python, BASIC

Introduction to Python

Python is a high-level language, which is used in designing, deploying, and testing at lots of places. It is consistently ranked among today’s most popular programming languages. It is also dynamic and object-oriented language but also works on procedural styles as well, and runs on all major hardware platforms. Python is an interpreted language.

How does Python Works?

Bytecode, also termed p-code, is a form of instruction set designed for efficient execution by a software interpreter

• First step is to write a Python program such as test.py
• Then using Python interpreter program is in built compiled and gets converted into byte code that is test.pyc.
• Python saves byte code like this as a startup speed optimization. The next time you run your program, Python will load the .pyc files and skip the compilation step, as long as you haven’t changed your source code since the byte code was last saved.

• Once your program has been compiled to byte code (or the byte code has been loaded from existing .pyc files), it is shipped off for execution to something generally known as the Python Virtual Machine
• Now byte code that is test.pyc is further converted into machine code using virtual machine such as (10101010100010101010)

• Finally Program is executed and output is displayed.

Python Interpreter

Python includes both interpreter and compiler which is implicitly invoked.

• In case of Python version 2, the Python interpreter compiles the source file such as file.py and keep it in same directory with an extension file.pyc
• In case of Python version 3 : the Python interpreter compiles the source file such as file.py and keep it in subdirectory __pycache__
• Python does not save the compiled bytecode when you run the script directly; rather, Python recompiles the script each time you run it.
• Python saves bytecode files only for modules you import however running Python command with -B flag avoids saving compiled bytecode to disk.
• You can also directly execute Python script in the Unix operating system if you add shebang inside your script.

#! /usr/bin/env python

Python Standard Library

Python standard library contains several well-designed Python modules for convenient reuse like representing data, processing text, processing data, interacting with operating systems and filesystems, and web programming. Python modules are basically Python Programs like a file (abc.py) that are imported.

There are some extension modules that allows Python code to access functionalities supplied by underlying OS or other software’s components such as GUI, database and network, XML parsing. You can also wrap existing C/C++ libraries into python extension modules.

Python Implementations

Python is more than a language, you can utilize the implementation of Python in many ways such as :

• CPython: CPython is an interpreter, compiler, set of built in and optional extension modules all coded in C language. Python code is converted into bytecode before interpreting it.

• IronPython: Python implementation for the Microsoft-designed Common Language Runtime (CLR), most commonly known as .NET, which is now open source and ported to Linux and macOS

• PyPy: PyPy is a fast and flexible implementation of Python, coded in a subset of Python itself, able to target several lower-level languages and virtual machines using advanced techniques such as type inferencing

• Jython: Python implementation for any Java Virtual Machine (JVM) compliant with Java 7 or better. With Jython, you can use all Java libraries and framework and it supports only v2 as of now.

• IPython: Enhances standard CPython to make it more powerful and convenient for interactive use. IPython extends the interpreter’s capabilities by allowing abbreviated function call syntax, using question mark to query an objects documentation etc.

Python Installation

Python Installation on Linux Machine

If you are working on the Latest platforms you will find Python already installed in the systems. At times Python is not installed but binaries are available in the system which you can install using RPM tool or using APT in Linux machines and for Windows use MSI( Microsoft Installer ) .

Python Installation on Windows Machine

Python can be installed in Windows with a few steps, and to install Python steps can be found here.

Python Installation on macOS

Python V2 comes installed on macOS but you should install the latest Python version always. The popular third-party macOS open-source package manager Homebrew offers, among many other packages, excellent versions of Python, both v2 and v3

• To install Homebrew, open Terminal or your favorite OS X terminal emulator and run

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

• Add homebrew directory at the top of your PATH environment variable.

export PATH="/usr/local/opt/python/libexec/bin:$PATH"

• Now install Python3 using the following commands.

brew install python3

• Verify the installation of Python using below command

Conclusion

In this tutorial you learnt everything which a beginner and a Devops engineer should know. This tutorial covered definition of python and some brilliant examples which will be enough to get you started with Python and for sure you will love it.

By Now, you are ready to build some exciting python programs. Hope you liked this tutorial and please share it with your friends.

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