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Variables and Data Types

In Python, variables are used to store information. You do not need to specify the type - Python detects it automatically. You can store numbers, text, boolean values, lists, and more.

Declaring Variables

# Example of variables
name = "John"         # String
age = 25           # Integer (int)
active = True          # Boolean value (True/False)
price = 19.99          # Decimal number (float)
☞Basic rules:
  • Variable names cannot start with a number.
  • Do not use spaces - you can use an underscore: nume_complet.
  • Python is case-sensitive: name ≠ Nume.

Data Types

Python has several data types. The most common are:

Type Example Description
int age = 30 Integer number
float price = 19.99 Decimal number
str name = "Anna" Text (string)
bool active = True True or False

Functions type() and isinstance()

The type() function returns the exact type of a variable. The isinstance() function checks whether a variable belongs to a specific type or group of types. 

# type()
x = 42
print(type(x))  # Displays: <class 'int'>

y = "Hello"
print(type(y))  # Displays: <class 'str'>

# isinstance()
z = 3.14
print(isinstance(z, float))  # Displays: True

a = True
print(isinstance(a, bool))  # Displays: True

b = "123"
print(isinstance(b, int))  # Displays: False
☞Note:
  • Use type() to see the exact type.
  • Use isinstance() for logical checks in your code.
  • You can check multiple types at once: isinstance(x, (int, float))

Type Conversions

Sometimes you need to convert one data type to another. Python provides simple functions for conversions. 

# Explicit conversions
x = 5
y = str(x)      # Becomes "5" - string
z = float(x)    # Becomes 5.0 - float
w = bool(x)     # Becomes True - any number ≠ 0 is considered True

# Reverse conversions
a = "10"
b = int(a)      # Becomes 10 - int

c = "3.14"
d = float(c)    # Becomes 3.14 - float

e = ""
f = bool(e)     # Becomes False - empty string is considered False
☞Important:
  • Conversion int("abc") will give an error - the string must contain only digits.
  • Conversion bool() returns False for: 0, "", [], None.

Functions input() and print()

The input() function receives data from the user as a string. The print() function displays information in the console. 

# Simple example
name = input("What is your name? ")     # Receives a string from the user
print("Hello,", name)                    # Displays the message
print(type(name))                        # Displays: <class 'str'>

# Conversion after input
age = int(input("How old are you? "))   # Converts the string to int
print("You are", age, "years old.")    # Displays the age

Simple Exercises

  1. Declare a variable an_nastere and display its data type.
  2. Convert an integer to float and display the result.
  3. Ask the user for a name and age, then display a personalized message.
# Exercise example
name = input("Name: ")
age = int(input("Age: "))
print("Hello,", name + "! You are", age, "years old.")

🧠 Quiz - Variables & Data Types in Python

Operators ➔

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