Python Notes #2 - Data types

x = 10 # x is an integer x = "Hello" # Now x is a string 

print(type(10)) # <class 'int'> print(type(3.14)) # <class 'float'> print(type("hello")) # <class 'str'> print(type([1, 2, 3])) # <class 'list'> print(type(None)) # <class 'NoneType'> 

# Integer (`int`) Methods x = -10 print(abs(x)) # 10 (Absolute value) print(bin(10)) # '0b1010' (Binary representation) print(hex(255)) # '0xff' (Hexadecimal representation) print(oct(8)) # '0o10' (Octal representation) print(int("1001", 2)) # 9 (Convert binary string to integer) # Floating-Point (`float`) Methods y = 3.14159 print(round(y, 2)) # 3.14 (Round to 2 decimal places) print(pow(2, 3)) # 8 (2^3, equivalent to 2**3) print(float("10.5")) # 10.5 (Convert string to float) print(int(4.7)) # 4 (Convert float to integer) print(y.is_integer()) # False (Checks if float has no decimal part) 

s = "hello world" print(s.upper()) # "HELLO WORLD" (Convert to uppercase) print(s.lower()) # "hello world" (Convert to lowercase) print(s.title()) # "Hello World" (Title case) print(s.strip()) # "hello world" (Removes leading/trailing spaces) print(s.replace("world", "Python")) # "hello Python" (Replace substring) print(s.split()) # ['hello', 'world'] (Split string into list) print("-".join(["Hello", "world"])) # "Hello-world" (Join list elements) print(s.find("world")) # 6 (Index of first occurrence of substring) print(s.count("l")) # 3 (Count occurrences of character) 

# Creating a list with 2 items my_list = [3, 1] # Adding Elements my_list.append(5) # [3, 1, 5] (Adds 5 at the end) my_list.insert(1, 10) # [3, 10, 1, 5] (Inserts 10 at index 1) my_list.extend([6, 7]) # [3, 10, 1, 5, 6, 7] (Concatenates another list) # Removing Elements my_list.pop() # [3, 10, 1, 5, 6] (Removes last element) my_list.pop(1) # [3, 1, 5, 6] (Removes element at index 1) my_list.remove(5) # [3, 1, 6] (Removes first occurrence of 5) my_list.clear() # [] (Removes all elements) # Rebuilding the list for further operations my_list = [3, 1] # Sorting & Reversing my_list.sort() # [1, 3] (Sorts the list in ascending order) my_list.reverse() # [3, 1] (Reverses the list) sorted_list = sorted(my_list) # Returns a new sorted list # Checking & Finding Elements print(3 in my_list) # True (Check existence) print(my_list.count(1)) # 1 (Count occurrences of 1) print(my_list.index(3)) # 0 (Find index of 3) # Copying the List copy_list = my_list.copy() # Creates a shallow copy of the list # List Length, Max, Min, and Sum print(len(my_list)) # 2 (Number of elements) print(max(my_list)) # 3 (Largest element) print(min(my_list)) # 1 (Smallest element) print(sum(my_list)) # 4 (Sum of all elements) # List Comprehension (Generating a List of Squares) squares = [x**2 for x in range(2)] # [0, 1] 

# Creating a list of squares squares = [x**2 for x in range(1, 6)] print(squares) # [1, 4, 9, 16, 25] # Filtering even numbers evens = [x for x in range(10) if x % 2 == 0] print(evens) # [0, 2, 4, 6, 8] # Creating a list of tuples pairs = [(x, x**2) for x in range(5)] print(pairs) # [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16)] 

t = (1, 2, 3, 2, 4) print(t.count(2)) # 2 (Count occurrences of 2) print(t.index(3)) # 2 (Find index of value 3) 

# Creating a tuple of squares squares_tuple = tuple(x**2 for x in range(1, 6)) print(squares_tuple) # (1, 4, 9, 16, 25) 

r = range(1, 10, 2) # Creates range from 1 to 9 with step 2 print(list(r)) # [1, 3, 5, 7, 9] (Convert range to list) print(r.start) # 1 (Start value) print(r.stop) # 10 (Stop value) print(r.step) # 2 (Step value) 

s = {1, 2, 3} # Adding and Removing Elements s.add(4) # {1, 2, 3, 4} s.remove(2) # {1, 3, 4} (Error if not found) s.discard(5) # No error if element doesn't exist s.clear() # {} (Removes all elements) # Set Operations s1 = {1, 2, 3} s2 = {3, 4, 5} print(s1.union(s2)) # {1, 2, 3, 4, 5} (Combine sets) print(s1.intersection(s2)) # {3} (Common elements) print(s1.difference(s2)) # {1, 2} (Elements in s1 but not in s2) print(s1.symmetric_difference(s2)) # {1, 2, 4, 5} (Elements in one set) # Membership Testing print(2 in s1) # True print(5 in s1) # False 

# Creating a set of squares squares_set = {x**2 for x in range(1, 6)} print(squares_set) # {1, 4, 9, 16, 25} # Extracting unique vowels from a string vowels = {char for char in "hello world" if char in "aeiou"} print(vowels) # {'o', 'e'} 

# Dictionary Keys, Values, and Items print(person.keys()) # dict_keys(['name', 'age']) print(person.values()) # dict_values(['Alice', 26]) print(person.items()) # dict_items([('name', 'Alice'), ('age', 26)]) # Checking if a Key Exists print("name" in person) # True print("email" in person) # False # Merging Dictionaries person.update({"country": "USA", "age": 27}) print(person) # {'name': 'Alice', 'age': 27, 'country': 'USA'} # Clearing a Dictionary person.clear() # {} 

# Creating a dictionary with squares of numbers squares = {x: x**2 for x in range(1, 6)} print(squares) # {1: 1, 2: 4, 3: 9, 4: 16, 5: 25} 

x = True y = False print(type(x)) # <class 'bool'> print(int(x), int(y)) # 1 0 

print(bool(0)) # False print(bool("")) # False print(bool([])) # False print(bool(100)) # True print(bool("Hello")) # True 

b = bytes([65, 66, 67]) # ASCII values for 'A', 'B', 'C' print(b) # b'ABC' print(b[0]) # 65 (Accessing byte value) 

ba = bytearray([65, 66, 67]) ba[1] = 68 # Modifying byte value print(ba) # bytearray(b'ADC') 

bv = memoryview(b"Hello") print(bv[1:4].tobytes()) # b'ell' (Slicing without copying data) 

x = 10 # int y = 2.5 # float result = x + y # int + float → float print(result, type(result)) # 12.5 <class 'float'> 

# Convert to Integer print(int(3.7)) # 3 (float → int) print(int("10")) # 10 (str → int) # Convert to Float print(float(5)) # 5.0 (int → float) # Convert to String print(str(100)) # "100" (int → str) # Convert to List, Tuple, Set print(list("abc")) # ['a', 'b', 'c'] print(tuple([1, 2, 3])) # (1, 2, 3) print(set([1, 2, 2, 3])) # {1, 2, 3} 

print(bool(0)) # False print(bool(10)) # True print(bool("")) # False print(bool("Python")) # True 

x = None print(x) # None print(type(x)) # <class 'NoneType'> def example(): pass # No return statement print(example()) # None value = None # Assign None until a real value is provided x = None if x is None: print("x has no value") # This runs 

from typing import List, Dict def add_numbers(a: int, b: int) -> int: return a + b def get_names() -> List[str]: return ["Alice", "Bob"] 

class Person: def __init__(self, name: str, age: int): self.name = name self.age = age p = Person("Alice", 25) print(p.name) # Alice 

from dataclasses import dataclass @dataclass class Employee: name: str salary: float e = Employee("Bob", 50000) print(e) # Employee(name='Bob', salary=50000) 

class Person: __slots__ = ['name', 'age'] def __init__(self, name, age): self.name = name self.age = age p = Person("Alice", 30) # p.address = "New York" # ❌ Error! `address` is not allowed. 

from typing import NamedTuple class Point(NamedTuple): x: int y: int p = Point(3, 4) print(p.x) # 3 # p.x = 5 # ❌ Error! NamedTuple is immutable. 

from collections import defaultdict, Counter # defaultdict (Default value for missing keys) d = defaultdict(int) d["a"] += 1 print(d) # {'a': 1} # Counter (Counts occurrences in an iterable) c = Counter("banana") print(c) # Counter({'a': 3, 'n': 2, 'b': 1}) 

from enum import Enum class Status(Enum): PENDING = 1 COMPLETED = 2 FAILED = 3 print(Status.PENDING) # Status.PENDING print(Status.PENDING.value) # 1