Python Notes for Interview

1. Basic Syntax:

# Comment
variable = value  # Variable assignment
print("Hello, World!")  # Print statement

2. Data Types:

string = "Hello"  # String
integer = 42  # Integer
float_number = 3.14  # Float
boolean = True  # Boolean
list = [1, 2, 3]  # List
tuple = (1, 2, 3)  # Tuple
dictionary = {"key": "value"}  # Dictionary

3. Control Flow:

if condition:
    # Code to execute if condition is true
elif condition2:
    # Code to execute if condition2 is true
else:
    # Code to execute if all conditions are false

for item in iterable:
    # Code to repeat for each item in iterable

while condition:
    # Code to execute while condition is true

try:
    # Code to try executing
except ExceptionType:
    # Code to handle exceptions of type ExceptionType
finally:
    # Code to execute regardless of exceptions

4. Functions:

def function_name(parameter1, parameter2):
    # Code block
    return result  # Optional return statement

result = function_name(argument1, argument2)  # Function call

5. Input and Output:

input_value = input("Enter a value: ")  # User input

file = open("filename.txt", "r")  # Open file for reading
content = file.read()  # Read file content
file.close()  # Close file

file = open("filename.txt", "w")  # Open file for writing
file.write("Hello, World!")  # Write to file
file.close()  # Close file

6. Modules and Libraries:

import module_name  # Import a module
from module_name import function_name  # Import a specific function
import module_name as alias  # Import with an alias

import random
random_number = random.randint(1, 10)  # Generate a random number

7. String Manipulation:

my_string = "Hello, World!"

length = len(my_string)  # Length of a string
uppercase = my_string.upper()  # Convert to uppercase
lowercase = my_string.lower()  # Convert to lowercase
substring = my_string[7:12]  # Extract substring
split_list = my_string.split(", ")  # Split string into a list

8. List Manipulation:

my_list = [1, 2, 3, 4, 5]

length = len(my_list)  # Length of a list
item = my_list[2]  # Access element by index
sliced_list = my_list[1:4]  # Extract a sublist
my_list.append(6)  # Add an element to the end
my_list.remove(3)  # Remove a specific element

9. Dictionary Manipulation:

my_dict = {"name": "John", "age": 30, "city": "New York"}

keys = my_dict.keys()  # Get dictionary keys
values = my_dict.values()  # Get dictionary values
item = my_dict["name"]  # Access value by key
my_dict["occupation"] = "Engineer"  # Add a new key-value pair
del my_dict["city"]  # Remove a key-value pair

10. File Handling:

with open("filename.txt", "r") as file:
    content = file.read()  # Read file content

with open("filename.txt", "w") as file:
    file.write("Hello, World!")  # Write to file

11. Error Handling:

try:
    # Code that may raise an exception
except ValueError as ve:
    # Code to handle ValueErrors
except FileNotFoundError:
    # Code to handle FileNotFoundError
else:
    # Code to execute if no exceptions are raised
finally:
    # Code to execute regardless of exceptions

12. Commonly Used Functions:

range(start, stop, step)  # Generate a sequence of numbers
len(sequence)  # Get the length of a sequence
type(object)  # Get the type of an object
sum(iterable)  # Calculate the sum of elements in an iterable
sorted(iterable)  # Sort elements in an iterable

13. Object-Oriented Programming (OOP):

class MyClass:
    def __init__(self, attribute):
        self.attribute = attribute

    def method(self):
        # Code block

my_object = MyClass("value")  # Create an instance of MyClass
my_object.method()  # Call a method of the object

14. Lambda Functions:

addition = lambda x, y: x + y  # Create a lambda function
result = addition(3, 4)  # Call the lambda function

15. Sets:

my_set = {1, 2, 3, 4, 5}

my_set.add(6)  # Add an element to the set
my_set.remove(3)  # Remove an element from the set
union_set = my_set.union({7, 8, 9})  # Perform set union
intersection_set = my_set.intersection({4, 5, 6})  # Perform set intersection

16. List Comprehensions:

numbers = [1, 2, 3, 4, 5]

squared_numbers = [x ** 2 for x in numbers]  # List comprehension
filtered_numbers = [x for x in numbers if x % 2 == 0]  # List comprehension with condition

17. DateTime:

from datetime import datetime

current_time = datetime.now()  # Get current date and time
formatted_time = current_time.strftime("%Y-%m-%d %H:%M:%S")  # Format datetime as a string

18. Math Functions:

import math

square_root = math.sqrt(25)  # Calculate square root
rounded_number = round(3.7)  # Round a number
absolute_value = abs(-5)  # Calculate absolute value

19. Regular Expressions:

import re

pattern = r"\d+"  # Regular expression pattern
matches = re.findall(pattern, "There are 123 apples")  # Find all matches in a string

20. Virtual Environments (venv):

# Set up a virtual environment
python3 -m venv myenv

# Activate the virtual environment
source myenv/bin/activate

# Install packages within the virtual environment
pip install package_name

# Deactivate the virtual environment
deactivate