Python Basics: Fundamental Operations and Code Snippets

Fundamental Operations

1. Print "Hello, World!": print("Hello, World!")

2. List comprehension to create a list of squares: squares = [x**2 for x in range(10)]

3. Dictionary comprehension to create a dictionary of squares: dict_comp = {x: x**2 for x in (2, 4, 6)}

4. Set comprehension to create a set of unique characters: set_comp = {x for x in 'abracadabra'}

5. Lambda expression for an anonymous addition function: add = lambda x, y: x + y

Data Processing

6. Filter even numbers from a range: even_numbers = list(filter(lambda x: x % 2 == 0, range(10)))

7. Map each number to its square: squared = list(map(lambda x: x**2, range(10)))

8. Sum of numbers 0‑9: sum_of_numbers = sum(range(10))

9. Maximum value in a list: max_number = max([1, 3, 5, 7, 9])

10. Minimum value in a list: min_number = min([2, 4, 6, 8, 10])

File Operations

11. Read all lines from a file: lines = [line.strip() for line in open('file.txt', 'r', encoding='utf-8')]

12. Write a line to a file: open('output.txt', 'w', encoding='utf-8').write('Hello, World!')

13. Check if a file exists: import os; file_exists = os.path.isfile('file.txt')

String Operations

14. Convert to uppercase: upper_str = "hello world".upper()

15. Convert to lowercase: lower_str = "HELLO WORLD".lower()

16. Palindrome check using slicing: is_palindrome = lambda s: s == s[::-1]

17. Replace a substring: replaced = "hello world".replace("world", "Python")

18. Split a string into a list: split_list = "apple,banana,cherry".split(',')

Mathematical Operations

19. Recursive factorial: factorial = lambda n: 1 if n == 0 else n * factorial(n-1)

20. Recursive Fibonacci: fibonacci = lambda n: n if n <= 1 else fibonacci(n-1) + fibonacci(n-2)

21. Greatest common divisor: from math import gcd; gcd_value = gcd(48, 18)

22. Least common multiple: from math import lcm; lcm_value = lcm(4, 6)

List Operations

23. Merge two lists: combined = [1, 2, 3] + [4, 5, 6]

24. Reverse a list using slicing: reversed_list = [1, 2, 3, 4, 5][::-1]

25. Find index of an element: index = [1, 2, 3, 4, 5].index(3)

26. Remove duplicates while preserving order: unique = list(dict.fromkeys([1, 2, 2, 3, 4, 4, 5]))

27. Check if a list is empty: my_list = []; is_empty = not my_list # returns True if empty, otherwise False

Dictionary Operations

28. Merge two dictionaries: merged = {**{'a': 1, 'b': 2}, **{'c': 3, 'd': 4}}

29. Get all keys: keys = list({'a': 1, 'b': 2}.keys())

30. Get all values: values = list({'a': 1, 'b': 2}.values())

31. Check key existence: key_exists = 'a' in {'a': 1, 'b': 2}

Set Operations

32. Union of two sets: union_set = set([1, 2, 3]).union(set([3, 4, 5]))

33. Intersection of two sets: intersection_set = set([1, 2, 3]) & set([2, 3, 4])

34. Difference of two sets: difference_set = set([1, 2, 3]) - set([2, 3, 4])

35. Symmetric difference of two sets: symmetric_difference_set = set([1, 2, 3]) ^ set([2, 3, 4])

Other Tips

36. Iterate two lists in parallel with zip : pairs = list(zip([1, 2, 3], ['a', 'b', 'c']))

37. Get index and value with enumerate : indexed = list(enumerate(['apple', 'banana', 'cherry']))

38. Check if any element satisfies a condition: any_true = any(x > 5 for x in [1, 2, 6, 4])

39. Check if all elements satisfy a condition: all_true = all(x < 10 for x in [1, 2, 3, 4, 9])

40. Sort a list: sorted_list = sorted([3, 1, 4, 1, 5, 9])

These one‑line snippets demonstrate Python's versatility and provide a quick reference for writing concise, efficient code.