Python Common Operations README

This README provides a quick reference for frequently used Python operations, such as accessing elements, string manipulations, sorting, searching, and more.

Table of Contents

1. Accessing Elements
2. String Manipulation
3. Sorting Lists
4. Searching in Collections
5. Mathematical Operations
6. Data Structures
7. File Handling
8. Error Handling
9. Miscellaneous

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Accessing Elements

Get the Last Element of a List

my_list = [10, 20, 30, 40, 50]
last_element = my_list[-1]  # Output: 50

Get the First Element of a List

first_element = my_list[0]  # Output: 10

Get a Subset of a List (Slicing)

subset = my_list[1:4]  # Output: [20, 30, 40]

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String Manipulation

Reverse a String

my_string = "Python"
reversed_string = my_string[::-1]  # Output: "nohtyP"

Convert to Uppercase

uppercase_string = my_string.upper()  # Output: "PYTHON"

Convert to Lowercase

lowercase_string = my_string.lower()  # Output: "python"

Check if a String Contains a Substring

if "Py" in my_string:
    print("Substring found!")  # Output: "Substring found!"

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Sorting Lists

Sort a List in Ascending Order

numbers = [5, 2, 9, 1, 5, 6]
sorted_numbers = sorted(numbers)  # Output: [1, 2, 5, 5, 6, 9]

Sort a List in Descending Order

sorted_desc = sorted(numbers, reverse=True)  # Output: [9, 6, 5, 5, 2, 1]

Sort a List In-Place

numbers.sort()  # numbers is now [1, 2, 5, 5, 6, 9]

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Searching in Collections

Check If an Element Exists in a List

fruits = ["apple", "banana", "cherry"]
if "banana" in fruits:
    print("Banana is in the list!")  # Output: "Banana is in the list!"

Find the Index of an Element

index = fruits.index("banana")  # Output: 1

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Mathematical Operations

Find the Maximum and Minimum Value

max_value = max(numbers)  # Output: 9
min_value = min(numbers)  # Output: 1

Calculate the Sum of a List

total = sum(numbers)  # Output: 28

Generate a Range of Numbers

num_range = list(range(1, 11))  # Output: [1, 2, 3, ..., 10]

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Data Structures

Create a Dictionary

person = {"name": "Alice", "age": 25, "city": "New York"}

Get a Value from a Dictionary

name = person.get("name")  # Output: "Alice"

Remove a Key from a Dictionary

person.pop("age")  # Removes "age" key from dictionary

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File Handling

Read a File

with open("example.txt", "r") as file:
    content = file.read()

Write to a File

with open("example.txt", "w") as file:
    file.write("Hello, Python!")

Append to a File

with open("example.txt", "a") as file:
    file.write("
Adding more content.")

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Error Handling

Try-Except Block

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

Catch Multiple Exceptions

try:
    x = int("text")
except (ValueError, TypeError):
    print("Invalid conversion!")

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Miscellaneous

Get Unique Elements from a List

unique_numbers = list(set(numbers))  # Output: [1, 2, 5, 6, 9]

Swap Two Variables

a, b = 5, 10
a, b = b, a  # Now a = 10, b = 5

List Comprehensions

squares = [x ** 2 for x in range(1, 6)]  # Output: [1, 4, 9, 16, 25]

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Conclusion

These are some of the most commonly used Python operations. Whether you're working with lists, strings, dictionaries, or files, these quick references will help you write efficient Python code.

Happy coding!