Python DSA Cheat-sheet for SuperHeros

# Python Cheat Sheet for Data Structures and Algorithms

# List and Tuple Operations

# Creating a list or tuple
my_list = [1, 2, 3, 4] # use square brackets for lists
my_tuple = (5, 6, 7, 8) # use parentheses for tuples

# Accessing elements by index
first = my_list[0] # get the first element of the list (index 0)
last = my_tuple[-1] # get the last element of the tuple (index -1)

# Slicing a list or tuple
sublist = my_list[1:3] # get a sublist from index 1 (inclusive) to index 3 (exclusive)
subtuple = my_tuple[:2] # get a subtuple from the beginning to index 2 (exclusive)
reversed_list = my_list[::-1] # get a reversed list using negative step

# Concatenating two lists or tuples
new_list = my_list + [9, 10] # create a new list by adding another list
new_tuple = my_tuple + (11, 12) # create a new tuple by adding another tuple

# Repeating a list or tuple
repeated_list = my_list * 2 # create a new list by repeating the original list twice
repeated_tuple = my_tuple * 3 # create a new tuple by repeating the original tuple three times

# Checking membership of an element
is_in_list = 3 in my_list # returns True if 3 is in the list, False otherwise
is_in_tuple = 9 in my_tuple # returns False if 9 is not in the tuple, True otherwise

# Iterating over a list or tuple
for x in my_list: # loop through each element x in the list
    print(x) # print x

for i, x in enumerate(my_tuple): # loop through each index i and element x in the tuple
    print(i, x) # print i and x

# Unpacking a list or tuple
a, b, c, d = my_list # assign each element of the list to a variable
e, f, g, h = my_tuple # assign each element of the tuple to a variable

# List methods (do not apply to tuples)
my_list.append(5) # add an element 5 at the end of the list
my_list.insert(2, 6) # insert an element 6 at index 2 of the list
my_list.remove(4) # remove the first occurrence of element 4 from the list
my_list.pop() # remove and return the last element of the list
my_list.pop(1) # remove and return the element at index 1 of the list
my_list.index(3) # return the index of the first occurrence of element 3 in the list
my_list.count(2) # return the number of times element 2 appears in the list
my_list.sort() # sort the list in ascending order (modify the original list)
my_list.reverse() # reverse the order of the list (modify the original list)
my_list.copy() # return a shallow copy of the list
my_list.clear() # remove all elements from the list

# Creating a dictionary
my_dict = {"name": "Alice", "age": 25, "gender": "female"} # use curly braces and colons for dictionaries

# Accessing values by keys
name = my_dict["name"] # get the value associated with the key "name"
age = my_dict.get("age") # get the value associated with the key "age" or None if not found

# Adding or updating key-value pairs
my_dict["email"] = "alice@gmail.com" # add a new key-value pair to the dictionary
my_dict["age"] = 26 # update the value associated with the key "age"

# Removing key-value pairs
del my_dict["gender"] # delete the key-value pair with the key "gender" from the dictionary
email = my_dict.pop("email") # remove and return the value associated with the key "email"
name, age = my_dict.popitem() # remove and return an arbitrary key-value pair as a tuple

# Checking membership of a key
is_in_dict = "name" in my_dict # returns True if "name" is a key in the dictionary, False otherwise

# Iterating over a dictionary
for key in my_dict: # loop through each key in the dictionary
    print(key) # print key

for value in my_dict.values(): # loop through each value in the dictionary
    print(value) # print value

for key, value in my_dict.items(): # loop through each key-value pair in the dictionary
    print(key, value) # print key and value

# Unpacking a dictionary into variables
name, age, gender = my_dict # assign each key of the dictionary to a variable
{"name": name, "age": age, "gender": gender} = my_dict # assign each value of the dictionary to a variable

my_dict.keys() # return a view object of the keys of the dictionary
my_dict.values() # return a view object of the values of the dictionary
my_dict.items() # return a view object of the key-value pairs of the dictionary
my_dict.update({"city": "New York", "age": 27}) # update the dictionary with another dictionary or iterable
my_dict.copy() # return a shallow copy of the dictionary
my_dict.clear() # remove all key-value pairs from the dictionary

# Creating a set
my_set = {1, 2, 3, 4} # use curly braces for sets (but no colons)
empty_set = set() # use the set() function to create an empty set

# Adding or removing elements
my_set.add(5) # add an element 5 to the set
my_set.remove(4) # remove an element 4 from the set (raises KeyError if not found)
my_set.discard(3) # remove an element 3 from the set (does nothing if not found)
my_set.pop() # remove and return an arbitrary element from the set (raises KeyError if empty)
my_set.clear() # remove all elements from the set

# Checking membership of an element
is_in_set = 2 in my_set # returns True if 2 is in the set, False otherwise

# Iterating over a set
for x in my_set: # loop through each element x in the set
    print(x) # print x

my_string = "   Hello, World!   "

# Length of a string
length = len(my_string)
print(length)  # Output: 19

# Splitting a string into a list
my_list = my_string.split(" ")
print(my_list)  # Output: ['', '', '', 'Hello,', 'World!', '', '', '']

# Joining elements of a list into a string
my_string = " ".join(my_list)
print(my_string)  # Output:    Hello, World!

# Checking if a substring exists in a string
if "Hello" in my_string:
    print("Substring found!")  # Output: Substring found!

# Replacing occurrences of a substring
new_string = my_string.replace("World", "Python")
print(new_string)  # Output:    Hello, Python!

# Converting a string to lowercase/uppercase
lowercase = my_string.lower()
uppercase = my_string.upper()
print(lowercase)  # Output:    hello, world!
print(uppercase)  # Output:    HELLO, WORLD!

# Checking if a string starts/ends with a specific substring
starts_with_hello = my_string.startswith("Hello")
ends_with_exclamation = my_string.endswith("!")
print(starts_with_hello)  # Output: False
print(ends_with_exclamation)  # Output: True

# Removing leading/trailing whitespace from a string
stripped_string = my_string.strip()
print(stripped_string)  # Output: Hello, World!

# Checking if a string is alphanumeric
is_alphanumeric = my_string.isalnum()
print(is_alphanumeric)  # Output: False

# Counting occurrences of a substring
count = my_string.count("Hello")
print(count)  # Output: 1