1. Reverse a String
def reverse_string(s):
return s[::-1]
# Example usage
print(reverse_string("Hello, World!")) # Output: !dlroW ,olleHExplanation: This function takes a string s and returns it reversed. The slicing method s[::-1] creates a new string that starts from the end towards the beginning.
2. Check if a Number is Prime
def is_prime(n):
if n <= 1:
return False
for i in range(2, int(n**0.5) + 1):
if n % i == 0:
return False
return True
# Example usage
print(is_prime(11)) # Output: TrueExplanation: This function checks if a number n is prime. It iterates from 2 to the square root of n, checking for divisibility. If any number divides n evenly, it returns False.
3. Count Vowels in a String
def count_vowels(s):
vowels = "aeiouAEIOU"
return sum(1 for char in s if char in vowels)
# Example usage
print(count_vowels("Hello, World!")) # Output: 3Explanation: This function counts the number of vowels in a string s. It uses a generator expression to iterate through the string and sums up the occurrences of vowels.
4. Flatten a Nested List
def flatten_list(nested_list):
return [item for sublist in nested_list for item in sublist]
# Example usage
print(flatten_list([[1, 2], [3, 4], [5]])) # Output: [1, 2, 3, 4, 5]Explanation: This function flattens a nested list using a list comprehension. It iterates through each sublist and each item within those sublists.
5. Generate Fibonacci Sequence
def fibonacci(n):
a, b = 0, 1
sequence = []
for _ in range(n):
sequence.append(a)
a, b = b, a + b
return sequence
# Example usage
print(fibonacci(10)) # Output: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]Explanation: This function generates the first n numbers in the Fibonacci sequence. It uses a loop to append the next number in the sequence to a list.
6. Find the Maximum Value in a List
def find_max(lst):
return max(lst)
# Example usage
print(find_max([1, 2, 3, 4, 5])) # Output: 5Explanation: This function returns the maximum value from a list using Python’s built-in max() function.
7. Remove Duplicates from a List
def remove_duplicates(lst):
return list(set(lst))
# Example usage
print(remove_duplicates([1, 2, 2, 3, 4, 4])) # Output: [1, 2, 3, 4]Explanation: This function removes duplicates from a list by converting it to a set (which inherently removes duplicates) and then back to a list.
8. Sort a Dictionary by Value
def sort_dict_by_value(d):
return dict(sorted(d.items(), key=lambda item: item[1]))
# Example usage
print(sort_dict_by_value({'a': 3, 'b': 1, 'c': 2})) # Output: {'b': 1, 'c': 2, 'a': 3}Explanation: This function sorts a dictionary by its values. It uses the sorted() function with a lambda function as the key.
9. Check for Palindrome
def is_palindrome(s):
return s == s[::-1]
# Example usage
print(is_palindrome("racecar")) # Output: TrueExplanation: This function checks if a string s is a palindrome by comparing it to its reverse.
10. Merge Two Dictionaries
def merge_dicts(dict1, dict2):
return {**dict1, **dict2}
# Example usage
print(merge_dicts({'a': 1}, {'b': 2})) # Output: {'a': 1, 'b': 2}Explanation: This function merges two dictionaries using the unpacking operator **, which combines their key-value pairs.
11. Calculate Factorial
def factorial(n):
if n == 0:
return 1
return n * factorial(n - 1)
# Example usage
print(factorial(5)) # Output: 120Explanation: This recursive function calculates the factorial of a number n. The base case is when n is 0, returning 1.
12. Find the Intersection of Two Lists
def list_intersection(lst1, lst2):
return list(set(lst1) & set(lst2))
# Example usage
print(list_intersection([1, 2, 3], [2, 3, 4])) # Output: [2, 3]Explanation: This function finds the intersection of two lists by converting them to sets and using the intersection operator &.
13. Convert Celsius to Fahrenheit
def celsius_to_fahrenheit(celsius):
return (celsius * 9/5) + 32
# Example usage
print(celsius_to_fahrenheit(0)) # Output: 32.0Explanation: This function converts a temperature from Celsius to Fahrenheit using the formula ( F = C \times \frac{9}{5} + 32 ).
14. Count Occurrences of an Element in a List
def count_occurrences(lst, element):
return lst.count(element)
# Example usage
print(count_occurrences([1, 2, 2, 3], 2)) # Output: 2Explanation: This function counts how many times a specific element appears in a list using the count() method.
15. Generate a Random Password
import random
import string
def generate_password(length=8):
characters = string.ascii_letters + string.digits + string.punctuation
return ''.join(random.choice(characters) for _ in range(length))
# Example usage
print(generate_password(12)) # Output: Random 12-character passwordExplanation: This function generates a random password of a specified length using letters, digits, and punctuation. It uses the random.choice() method to select characters.
16. Find the Length of a String
def string_length(s):
return len(s)
# Example usage
print(string_length("Hello, World!")) # Output: 13Explanation: This function returns the length of a string s using the built-in len() function.
17. Check if a String Contains Only Digits
def is_all_digits(s):
return s.isdigit()
# Example usage
print(is_all_digits("12345")) # Output: TrueExplanation: This function checks if a string s contains only digits using the isdigit() method.
18. Find the Index of an Element in a List
def find_index(lst, element):
return lst.index(element)
# Example usage
print(find_index([1, 2, 3, 4], 3)) # Output: 2Explanation: This function returns the index of the first occurrence of element in a list using the index() method.
19. Remove Whitespace from a String
def remove_whitespace(s):
return s.replace(" ", "")
# Example usage
print(remove_whitespace("Hello, World!")) # Output: Hello,World!Explanation: This function removes all whitespace from a string s using the replace() method.
20. Create a Simple Countdown Timer
import time
def countdown_timer(seconds):
for i in range(seconds, 0, -1):
print(i)
time.sleep(1)
print("Time's up!")
# Example usage
# countdown_timer(5) # Uncomment to runExplanation: This function creates a countdown timer that counts down from a specified number of seconds. It uses time.sleep(1) to pause for one second between counts.
Here are additional Python code snippets along with detailed explanations for each, continuing from the previous list:
21. Simple Calculator
import operator
calculator = {
"+": operator.add,
"-": operator.sub,
"/": operator.truediv,
"*": operator.mul,
"**": pow
}
print(calculator['-'](10, 1)) # Output: 9Explanation: This snippet creates a simple calculator using the operator module, which provides function equivalents for standard arithmetic operations. The calculator dictionary maps string representations of operators to their corresponding functions. The example demonstrates subtraction by calling the function associated with the '-' key.
22. Print the String N Times
n = 5
s = "hello"
print(s * n)Explanation: This code snippet prints the string s repeated n times. In this case, it will output "hello" five times in a row, resulting in "hellohellohellohellohello".
23. Shuffle a List
from random import shuffle
foo = [1, 2, 3, 4]
shuffle(foo)
print(foo) # Output: Randomly shuffled list, e.g., [1, 4, 3, 2]Explanation: This snippet uses the shuffle function from the random module to randomly rearrange the elements of the list foo. Each time you run this code, the output will be a different random order of the list elements.
24. Set Difference
# Using set.difference() method
x = {"apple", "banana", "cherry"}
y = {"google", "microsoft", "apple"}
z = x.difference(y)
print(z) # Output: {'banana', 'cherry'}Explanation: This code demonstrates how to find the difference between two sets using the difference() method. The result z contains elements that are in set x but not in set y.
# Using '-' as a shortcut
a = {"apple", "banana", "cherry"}
b = {"google", "microsoft", "apple"}
myset = a - b
print(myset) # Output: {'banana', 'cherry'}Explanation: This snippet shows an alternative way to find the difference between two sets using the - operator, which is a shorthand for the difference() method.
25. Capitalize First Letters of Words
s = "hello world"
print(s.title()) # Output: Hello WorldExplanation: This code uses the title() method to capitalize the first letter of each word in the string s. The output will be "Hello World".
26. Swap Values
def swap(a, b):
return b, a
a, b = 1, 2
print(swap(a, b)) # Output: (2, 1)Explanation: This function swaps the values of a and b and returns them as a tuple. The example shows how to call the function and print the swapped values.
27. Get Default Value for Missing Keys
d = {'a': 1, 'b': 2}
print(d.get('c', 3)) # Output: 3Explanation: This code uses the get() method of dictionaries to retrieve the value for the key 'c'. Since 'c' does not exist in the dictionary d, it returns the default value 3.
Here are 20 more Python code snippets with detailed explanations for each, expanding your repertoire of useful functions and techniques:
28. Find the Minimum Value in a List
def find_min(lst):
return min(lst)
# Example usage
print(find_min([5, 3, 8, 1, 4])) # Output: 1Explanation: This function returns the minimum value from a list using Python’s built-in min() function.
29. Generate a List of Squares
def generate_squares(n):
return [x**2 for x in range(n)]
# Example usage
print(generate_squares(5)) # Output: [0, 1, 4, 9, 16]Explanation: This function generates a list of squares of numbers from 0 to n-1 using a list comprehension.
30. Check if a String is an Anagram
def is_anagram(s1, s2):
return sorted(s1) == sorted(s2)
# Example usage
print(is_anagram("listen", "silent")) # Output: TrueExplanation: This function checks if two strings are anagrams by sorting their characters and comparing the results.
31. Convert a List to a Set
def list_to_set(lst):
return set(lst)
# Example usage
print(list_to_set([1, 2, 2, 3, 4])) # Output: {1, 2, 3, 4}Explanation: This function converts a list to a set, automatically removing duplicates.
32. Get the Current Date and Time
from datetime import datetime
def current_datetime():
return datetime.now()
# Example usage
print(current_datetime()) # Output: Current date and timeExplanation: This function returns the current date and time using the datetime module.
33. Find the Length of a List
def list_length(lst):
return len(lst)
# Example usage
print(list_length([1, 2, 3, 4, 5])) # Output: 5Explanation: This function returns the number of elements in a list using the built-in len() function.
34. Remove an Element from a List
def remove_element(lst, element):
lst.remove(element)
return lst
# Example usage
print(remove_element([1, 2, 3, 4], 3)) # Output: [1, 2, 4]Explanation: This function removes the first occurrence of element from the list lst using the remove() method.
35. Check if a Number is Even
def is_even(n):
return n % 2 == 0
# Example usage
print(is_even(4)) # Output: TrueExplanation: This function checks if a number n is even by checking if the remainder when divided by 2 is zero.
36. Convert a List of Strings to Uppercase
def to_uppercase(lst):
return [s.upper() for s in lst]
# Example usage
print(to_uppercase(["hello", "world"])) # Output: ['HELLO', 'WORLD']Explanation: This function converts each string in the list lst to uppercase using a list comprehension and the upper() method.
37. Check if a String Contains a Substring
def contains_substring(s, substring):
return substring in s
# Example usage
print(contains_substring("Hello, World!", "World")) # Output: TrueExplanation: This function checks if a string s contains a specified substring using the in operator.
38. Calculate the Sum of a List
def sum_of_list(lst):
return sum(lst)
# Example usage
print(sum_of_list([1, 2, 3, 4])) # Output: 10Explanation: This function calculates the sum of all elements in a list using the built-in sum() function.
39. Create a Dictionary from Two Lists
def lists_to_dict(keys, values):
return dict(zip(keys, values))
# Example usage
print(lists_to_dict(['a', 'b', 'c'], [1, 2, 3])) # Output: {'a': 1, 'b': 2, 'c': 3}Explanation: This function creates a dictionary by zipping together two lists, one for keys and one for values.
40. Check if a Year is a Leap Year
def is_leap_year(year):
return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)
# Example usage
print(is_leap_year(2024)) # Output: TrueExplanation: This function checks if a given year is a leap year based on the rules of the Gregorian calendar.
41. Find the GCD of Two Numbers
import math
def gcd(a, b):
return math.gcd(a, b)
# Example usage
print(gcd(12, 15)) # Output: 3Explanation: This function calculates the greatest common divisor (GCD) of two numbers using the gcd() function from the math module.
42. Create a List of Even Numbers
def even_numbers(n):
return [x for x in range(n) if x % 2 == 0]
# Example usage
print(even_numbers(10)) # Output: [0, 2, 4, 6, 8]Explanation: This function generates a list of even numbers from 0 to n-1 using a list comprehension.
43. Replace a Substring in a String
def replace_substring(s, old, new):
return s.replace(old, new)
# Example usage
print(replace_substring("Hello, World!", "World", "Python")) # Output: Hello, Python!Explanation: This function replaces occurrences of old substring with new in the string s using the replace() method.
44. Capitalize the First Letter of a String
def capitalize_first_letter(s):
return s.capitalize()
# Example usage
print(capitalize_first_letter("hello")) # Output: HelloExplanation: This function capitalizes the first letter of the string s using the capitalize() method.
45. Merge Two Lists
def merge_lists(lst1, lst2):
return lst1 + lst2
# Example usage
print(merge_lists([1, 2], [3, 4])) # Output: [1, 2, 3, 4]Explanation: This function merges two lists by concatenating them using the + operator.
46. Check if a String is Numeric
def is_numeric(s):
return s.isnumeric()
# Example usage
print(is_numeric("12345")) # Output: TrueExplanation: This function checks if a string s consists only of numeric characters using the isnumeric() method.
47. Find the Product of a List
from functools import reduce
def product_of_list(lst):
return reduce(lambda x, y: x * y, lst)
# Example usage
print(product_of_list([1, 2, 3, 4])) # Output: 24Explanation: This function calculates the product of all elements in a list using reduce() from the functools module with a lambda function.
48. Count Words in a String
def count_words(s):
return len(s.split())
# Example usage
print(count_words("Hello, World!")) # Output: 2Explanation: This function counts the number of words in a string s by splitting it into a list of words and counting the length of that list.
49. Flatten a List of Lists Using Recursion
def flatten(nested_list):
flat_list = []
for item in nested_list:
if isinstance(item, list):
flat_list.extend(flatten(item))
else:
flat_list.append(item)
return flat_list
# Example usage
print(flatten([[1, 2], [3, [4, 5]], 6])) # Output: [1, 2, 3, 4, 5, 6]Explanation: This recursive function flattens a list of lists, handling any level of nesting.
50. Create a Simple GUI with Tkinter
import tkinter as tk
def on_button_click():
print("Button clicked!")
root = tk.Tk()
button = tk.Button(root, text="Click Me", command=on_button_click)
button.pack()
root.mainloop()Explanation: This code creates a simple graphical user interface (GUI) using the tkinter module. When the button is clicked, it executes the on_button_click() function, which prints a message to the console.
51 Contains Duplicate
class Solution:
def containsDuplicate(self, nums: List[int]) -> bool:
st = set()
for n in nums:
if n in st:
return True
st.add(n)
return FalseExplanation: This code defines a method containsDuplicate which determines if there are any duplicate values in a list of integers. Here’s a breakdown of how it works:
52 Sorting a string
Sorting a string in Python involves arranging its characters in a specific order, typically in alphabetical order. Here are a few methods to achieve this:
Using sorted() Function
The sorted() function returns a sorted list of the string’s characters. You can then join these characters back into a string using join(). Here’s how you can do it:
s = "example"
sorted_string = ''.join(sorted(s))
print(sorted_string) # Output: aeelmpxSorting with Case Insensitivity
If you want to sort the string in a case-insensitive manner, you can use the key parameter with str.lower or str.upper:
s = "Example"
sorted_string = ''.join(sorted(s, key=str.lower))
print(sorted_string) # Output: aeElmpxReverse Sorting
To sort the string in descending order, you can use the reverse parameter:
s = "example"
sorted_string = ''.join(sorted(s, reverse=True))
print(sorted_string) # Output: xpmleeaPrint Binary
def print_binary(num):
"""
Print the binary representation of an integer (32-bit).
The left side is the higher bits, and the right side is the lower bits.
"""
for i in range(31, -1, -1):
# This line can be written as:
# print("1" if (num & (1 << i)) != 0 else "0", end="")
# But it cannot be written as:
# print("1" if (num & (1 << i)) == 1 else "0", end="")
# Because if the i-th bit of num is 1, then (num & (1 << i)) is 2^i, not necessarily 1.
# For example, num = 0010011
# The 0th, 1st, and 4th bits of num are 1.
# (num & (1 << 4)) == 16 (not 1), indicating that the 4th bit of num is 1.
print("0" if (num & (1 << i)) == 0 else "1", end="")
print()These methods utilize Python’s built-in functions to efficiently sort the characters in a string, allowing you to easily customize the order based on your requirements.