Learning Python for Devops day -1

Hello everyone, this is Abhishek Pol, and welcome to my first blog about learning AWS DevOps. I started my journey around two months ago, and I believe it's never too late to share your experiences. Without further ado, let me share what I learned today.

What is Python Python?

Python is an interpreted, object-oriented, high-level programming language. Its simple and easy-to-learn syntax makes it easy to read and maintain. Python supports modules and packages, which help in organizing code and reusing it. The Python interpreter and its large standard library are free to use and available for all major platforms.

Pre-requisites

• Indentation

• Declaration of variable not required (automatically derive the data type)

Python Shell

We can use any of the following Python Shells to understand this language:

1. Python Online Shell

   • Navigate to Python Online Shell in your browser: https://www.python.org/shell/

2. Login to EC2 and Install Python3 using yum

   • Login to your EC2 instance.

   • Install Python3 using the following command:

       sudo yum install python3
     

   • To open the Python Interpreter, enter:

       python3
     

Values and Types

• A value is one of the basic things a program works with, like a letter or a number.

• To get the type of a value, you can use the type() function in Python:

    >>> type('Hello, World!')
    <class 'str'>
    >>> type(17)
    <class 'int'>
    >>> type('17')
    <class 'str'>
    >>> type(3.2)
    <class 'float'>
    >>> type('3.2')
    <class 'str'>
  

• This is similar to the echo command in bash:

    print("Hello, World!")
  

  FYI: Always remember, in the above example, whatever we write inside the print brackets gets printed when we execute the command. If we want to check the type, for example, if it's an integer or a string (integer means numbers and string means letters or alphabets), we use the type() command. Inside the brackets, whatever we write, it shows its type.

• variables

• Variables are used to store values. An assignment statement creates new variables and gives them values:

    # Assigning a value to a variable
    msg = "Hello world!"
  
    # Checking the type of the variable
    print(type(msg))
  
    # Printing the value of the variable
    print(msg)
  

  Concatenation (combining strings):

    # Assigning values to variables
    first = 'AWS'
    last = 'Devops'
  
    # Combining strings with a space in between
    full_name = first + ' ' + last
  
    # Printing the combined string
    print(full_name)
  

  FYI: Concatenation is just combining strings, like making a sentence. In the example above, you can see we assigned values to two variables, and each variable holds a string because it contains letters. To join the two words, we use the + symbol. You can also see ' ' in the code, which adds a space between the two words. So, for anyone reading this blog, here's a little homework: try printing full_name and see the output. Keep experimenting with more words to understand it better!

  Comments

• in Python start with the # symbol. This comment contains useful information that is not in the code:

    # Assigning a value to the variable with a comment
    v = 5  # velocity in meters/second
  
    # Printing the value of the variable
    print(v)
  

  Boolean Expressions

  A boolean expression is an expression that evaluates to either true or false. The following examples use the == operator, which compares two operands and returns True if they are equal and False otherwise:

    >>> 5 == 5
    True
  
    >>> 5 == 6
    False
  

  True and False are special values that belong to the type bool; they are not strings:

    >>> type(True)
    <class 'bool'>
  
    >>> type(False)
    <class 'bool'>
  

  The == operator is one of several relational operators. Here are the others:

  • x != y : x is not equal to y

  • x > y : x is greater than y

  • x < y : x is less than y

  • x >= y : x is greater than or equal to y

  • x <= y : x is less than or equal to y

FYI

Interpreter vs Compiler

Python and Java

Java

// Your First Program
class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World inside main function");
    }
    // This line will cause a compilation error because it's outside the main function
    // System.out.println("Hello, World! outside main function");
}

To install Java, use:

sudo yum install java-devel

If you have Java installed on your machine/server, you can execute:

javac HelloWorld.java

to compile the Java code. This will create a HelloWorld.class file. The program can be executed with:

java HelloWorld

Python

Python follows an indentation approach and does not use curly brackets.

# Example of an if-else statement in Python
x = 10

if x > 5:
    print("x is greater than 5")
else:
    print("x is not greater than 5")

# This line is outside the if-else block
print("This line is outside the if-else block")

Key Differences:

• Java uses curly brackets {} to define code blocks.

• Python uses indentation to define code blocks.

• Java requires a main function to execute code.

• Python executes code directly without the need for a main function.

NOTE: Always remember, when using if or any condition in Python, you must use a colon : at the end of the statement. For indentation, use the Tab key, not the space bar. This ensures your output prints correctly. If you nest another loop or condition inside an if statement, you need to use two tabs to avoid any indentation errors.

Conditional Execution

Conditional statements allow us to write useful programs by checking conditions and changing the behavior of the program accordingly. The simplest form is the if statement:

x = 5
if x > 0:
    print('x is positive')

The boolean expression after if is called the condition. If it is true, then the indented statement gets executed. If not, nothing happens.

Another example of if:

age = 21
if age >= 18:
    print("You can vote!")

If-elif-else Statements

age = 21

if age < 4:
    ticket_price = 0
elif age < 18:
    ticket_price = 10
else:
    ticket_price = 15

print("Ticket price is", ticket_price)

Steps to Run the Code

1. Create a file named ticket_price.py.

2. Write the above code in the file.

3. Run it with the command:

    python ticket_price.py
   

   FYI: When writing a script in Linux, we use the vi command. Similarly, in Python, we use vi followed by the name of the script we want to execute, ending with .py. After writing your script, use :wq to save and exit. On an AWS EC2 Python server, use the name you assigned, like in the example above (ticket_price.py). In Linux, we use bash or ./ to execute commands. Here, we use python or python3 depending on which version of Python you have installed.

Lists

A list stores a series of items in a particular order. You can access items using an index or within a loop. Lists are mutable, meaning you can change their content. In a list, the first value is at index 0.

Example of List Operations

# Creating a list of bikes
bikes = ['Apache', 'Suzuki', 'Pulsar']

# Modifying an item in the list
bikes[1] = 'BMW'

# Checking the type of the list
print(type(bikes))

# Getting the first item in the list
first_bike = bikes[0]
print(first_bike)

# Attempting to access an out-of-range index
# This will raise an IndexError
# bikes[3]

# Getting the last item in the list
last_bike = bikes[-1]
print(last_bike)

# Getting the length of the list
print(len(bikes))

# Iterating through the list
for bike in bikes:
    print(bike)

Adding Items to a List

# Creating an empty list
bikes = []

# Adding items to the list
bikes.append('Apache')
bikes.append('Suzuki')
bikes.append('Pulsar')

# Checking the length of the list
print(len(bikes))

Slicing a List

# Creating a list of AWS topics
aws_topics = ['ec2', 's3', 'rds', 'lambda']

# Slicing the list to get the first two items
first_two = aws_topics[:2]
print(first_two)

# Creating a copy of the list
aws_topics_copy = aws_topics[:]
print(aws_topics_copy)

# Various slicing examples
print(aws_topics[:])       # ['ec2', 's3', 'rds', 'lambda']
print(aws_topics[0:1])     # ['ec2']
print(aws_topics[0:2])     # ['ec2', 's3']
print(aws_topics[:2])      # ['ec2', 's3']
print(aws_topics[1:3])     # ['s3', 'rds']

Summary

• Lists are mutable and can store a series of items.

• Access items using an index, starting from 0.

• Use slicing to get a subset of the list.

• Use loops to iterate through the list.

• Use append() to add items to the list.

• Use len() to get the length of the list.

Tuples

Tuples are immutable. A tuple is a sequence of values. The values can be of any type, and they are indexed by integers, so in that respect, tuples are a lot like lists. Syntactically, a tuple is a comma-separated list of values:

>>> t = 'a', 'b', 'c', 'd', 'e'

Although it is not necessary, it is common to enclose tuples in parentheses:

>>> t = ('a', 'b', 'c', 'd', 'e')

Another way to create a tuple is by using the built-in function tuple(). With no argument, it creates an empty tuple:

>>> t = tuple()
>>> print(t)
()

You can also create a tuple with values:

>>> t = ('a', 'b', 'c', 'd', 'e')
>>> print(t[0])
'a'
>>> print(t[1:3])
('b', 'c')

But if you try to modify one of the elements of the tuple, you get an error:

>>> t[0] = 'A'
TypeError: 'tuple' object does not support item assignment

Thank you so much for reading my first blog! I hope you learned a lot with me, and yes, keep learning and keep motivating everyone. Have a wonderful day!