Master Python Basics: Variables, Loops, Data Structures, and OOP Explained

Python is a high‑level, readable programming language created by Guido van Rossum. It combines interpreted, compiled, interactive, and object‑oriented features, making it suitable for data science, web development, and machine learning.

Variables

Assign values to variables using the = operator:

one = 1

two = 2

some_number = 10000

Variables can hold booleans, strings, floats, and other data types:

# booleans
true_boolean = True
false_boolean = False

# string
my_name = "Leandro Tk"

# float
book_price = 15.80

Conditional Statements

Use if, elif, and else to control flow based on conditions:

if True:
    print("Hello Python If")

if 2 > 1:
    print("2 is greater than 1")

if 1 > 2:
    print("1 is greater than 2")
else:
    print("1 is not greater than 2")

if 1 > 2:
    print("1 is greater than 2")
elif 2 > 1:
    print("2 is greater than 1")
else:
    print("1 is equal to 2")

Loops

While loop repeats while a condition is true:

num = 1
while num <= 10:
    print(num)
    num += 1

Infinite loop example with a boolean flag:

loop_condition = True
while loop_condition:
    print("Loop Condition keeps: %s" % (loop_condition))
    loop_condition = False

For loop iterates over a range or a collection:

for i in range(1, 11):
    print(i)

bookshelf = ["The Effective Engineer", "The 4 Hour Work Week", "Zero to One", "Lean Startup", "Hooked"]
for book in bookshelf:
    print(book)

Lists (Arrays)

Create and access list elements by index (starting at 0):

my_integers = [1, 2, 3, 4, 5]
print(my_integers[0])  # 1
print(my_integers[1])  # 2

my_integers = [5, 7, 1, 3, 4]
print(my_integers[0])  # 5
print(my_integers[1])  # 7
print(my_integers[4])  # 4

Append elements to a list:

bookshelf = []
bookshelf.append("The Effective Engineer")
bookshelf.append("The 4 Hour Work Week")
print(bookshelf[0])  # The Effective Engineer
print(bookshelf[1])  # The 4 Hour Work Week

Dictionaries (Key‑Value Mapping)

Define a dictionary with key‑value pairs:

dictionary_example = {
    "key1": "value1",
    "key2": "value2",
    "key3": "value3"
}
print(dictionary_example["key1"])  # value1

Access and modify entries:

dictionary_tk = {
    "name": "Leandro",
    "nickname": "Tk",
    "nationality": "Brazilian"
}
print("My name is %s" % (dictionary_tk["name"]))
print("But you can call me %s" % (dictionary_tk["nickname"]))

# Add a new key
dictionary_tk["age"] = 24
print(dictionary_tk)  # {'name': 'Leandro', 'nickname': 'Tk', 'nationality': 'Brazilian', 'age': 24}

Classes and Objects

Define a class with an initializer and methods:

class Vehicle:
    def __init__(self, number_of_wheels, type_of_tank, seating_capacity, maximum_velocity):
        self.number_of_wheels = number_of_wheels
        self.type_of_tank = type_of_tank
        self.seating_capacity = seating_capacity
        self.maximum_velocity = maximum_velocity

    def make_noise(self):
        print('VRUUUUUUUM')

# Create an instance
tesla_model_s = Vehicle(4, 'electric', 5, 250)
print(tesla_model_s.number_of_wheels)  # 4

tesla_model_s.make_noise()  # VRUUUUUUUM

Use @property to create getters and setters:

class Vehicle:
    def __init__(self, number_of_wheels, type_of_tank, seating_capacity, maximum_velocity):
        self._number_of_wheels = number_of_wheels
        self.type_of_tank = type_of_tank
        self.seating_capacity = seating_capacity
        self.maximum_velocity = maximum_velocity

    @property
    def number_of_wheels(self):
        return self._number_of_wheels

    @number_of_wheels.setter
    def number_of_wheels(self, number):
        self._number_of_wheels = number

car = Vehicle(4, 'electric', 5, 250)
print(car.number_of_wheels)  # 4
car.number_of_wheels = 2
print(car.number_of_wheels)  # 2

Encapsulation

Public attributes are accessed directly, while private attributes (prefixed with an underscore) are accessed via methods:

class Person:
    def __init__(self, first_name, email):
        self.first_name = first_name          # public
        self._email = email                  # private

    def update_email(self, new_email):
        self._email = new_email

    def email(self):
        return self._email

p = Person('TK', '[email protected]')
print(p.first_name)   # TK
print(p.email())      # [email protected]
p.update_email('[email protected]')
print(p.email())      # [email protected]

Inheritance

Define a base class Car and a subclass ElectricCar that inherits its attributes:

class Car:
    def __init__(self, number_of_wheels, seating_capacity, maximum_velocity):
        self.number_of_wheels = number_of_wheels
        self.seating_capacity = seating_capacity
        self.maximum_velocity = maximum_velocity

class ElectricCar(Car):
    def __init__(self, number_of_wheels, seating_capacity, maximum_velocity):
        super().__init__(number_of_wheels, seating_capacity, maximum_velocity)

my_electric_car = ElectricCar(4, 5, 250)
print(my_electric_car.number_of_wheels)      # 4
print(my_electric_car.seating_capacity)    # 5
print(my_electric_car.maximum_velocity)    # 250

Source: Machine Heart (机器之心) Original article: Learning Python from Zero to Hero