Python Basics - Variables, Types, and Syntax

Welcome to Python basics! This is where your Python journey begins. We'll learn about variables, data types, and how to write basic Python code. Python is known for being simple and readable - you'll see why!

Variables in Python

Variables store data. In Python, creating variables is super simple:

name = "John"
age = 25
height = 5.9

That's it! No need to declare types - Python figures it out automatically.

Variable Naming Rules

• Can contain letters, numbers, and underscores
• Must start with a letter or underscore
• Case-sensitive (name and Name are different)
• Can't use Python keywords (like if, for, def)

# Good variable names
user_name = "John"
user_age = 25
total_count = 100
 
# Bad variable names
2name = "John"  # Can't start with number
user-name = "John"  # Can't use hyphens

Data Types in Python

Python has several built-in types:

Numbers

# Integers (whole numbers)
age = 25
count = -10
 
# Floats (decimal numbers)
price = 19.99
temperature = -5.5
 
# Complex numbers (advanced)
complex_num = 3 + 4j

Strings

Strings are text:

name = "John"
message = 'Hello, World!'
multiline = """This is
a multiline
string"""

Booleans

True or False values:

is_active = True
is_done = False

None

Represents "nothing":

value = None

Type Checking

You can check a variable's type:

name = "John"
print(type(name))  # <class 'str'>
 
age = 25
print(type(age))   # <class 'int'>

Basic Operations

Arithmetic Operations

a = 10
b = 3
 
print(a + b)  # 13 (addition)
print(a - b)  # 7 (subtraction)
print(a * b)  # 30 (multiplication)
print(a / b)  # 3.333... (division)
print(a // b) # 3 (floor division)
print(a % b)  # 1 (modulo/remainder)
print(a ** b) # 1000 (exponentiation)

String Operations

first_name = "John"
last_name = "Doe"
 
# Concatenation
full_name = first_name + " " + last_name
print(full_name)  # "John Doe"
 
# Repetition
greeting = "Hello! " * 3
print(greeting)  # "Hello! Hello! Hello! "
 
# Length
print(len(full_name))  # 8

Comparison Operations

a = 10
b = 5
 
print(a == b)  # False (equal)
print(a != b)  # True (not equal)
print(a > b)   # True (greater than)
print(a < b)   # False (less than)
print(a >= b)  # True (greater than or equal)
print(a <= b)  # False (less than or equal)

Input and Output

Printing Output

print("Hello, World!")
print("Name:", name)
print(f"Age: {age}")  # f-string (formatted string)

Getting Input

name = input("Enter your name: ")
age = int(input("Enter your age: "))  # Convert to integer

Type Conversion

Convert between types:

# String to number
age_str = "25"
age = int(age_str)
 
# Number to string
age = 25
age_str = str(age)
 
# Float to int
price = 19.99
price_int = int(price)  # 19 (truncates)

Comments

Comments help explain your code:

# This is a single-line comment
 
"""
This is a
multi-line comment
"""
 
# Comments are ignored by Python

Visual Explanation: Python Variable Assignment

Here's how variables work:

Variable Assignment:
┌─────────────────────────────┐
│ name = "John"               │
│                             │
│ 1. Python creates variable │
│ 2. Assigns value "John"    │
│ 3. Determines type: string │
└─────────────────────────────┘
 
Memory:
┌──────────────┐
│ name         │
│ ────────────│
│ "John"       │
│ (string)     │
└──────────────┘

Frequently Asked Questions (FAQ)

Q1: Do I need to declare variable types in Python?

A: No! Python is dynamically typed. You just assign values, and Python figures out the types automatically. This makes Python code shorter and easier to write.

Q2: Can I change a variable's type?

A: Yes! Python variables can change types:

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

This is different from statically typed languages.

Q3: What's the difference between = and ==?

A:

• = - Assignment (assigns value to variable)
• == - Comparison (checks if values are equal)

x = 5      # Assign 5 to x
x == 5     # Check if x equals 5 (returns True)

Q4: What are f-strings?

A: F-strings (formatted string literals) let you embed expressions in strings:

name = "John"
age = 25
message = f"My name is {name} and I'm {age} years old"

They're the modern way to format strings in Python!

Q5: How do I check if a variable exists?

A: Use in locals() or in globals():

if 'name' in locals():
    print("Variable exists")

Q6: What's the difference between / and //?

A:

• / - Regular division (returns float)
• // - Floor division (returns integer, rounds down)

10 / 3   # 3.333...
10 // 3  # 3

Q7: Can variable names have spaces?

A: No! Use underscores instead:

user_name = "John"  # Good
user name = "John"  # Error!

Q8: What happens if I use a variable before assigning it?

A: You'll get a NameError:

print(x)  # NameError: name 'x' is not defined
x = 10

Q9: Can I use keywords as variable names?

A: No! Python keywords are reserved:

if = 10  # SyntaxError: invalid syntax

Q10: What's the difference between single and double quotes?

A: No difference for strings! Use whichever you prefer:

name1 = "John"
name2 = 'John'
# Both are the same

Use double quotes if your string contains single quotes, and vice versa.

Next Steps

Now that you understand Python basics, here's what to learn next:

• Next: Learn about Python Data Structures - Lists, dictionaries, tuples, and sets
• Explore Python Functions - Write reusable code blocks
• Understand Python Control Flow - If statements, loops, and more
• Master Python Strings - Advanced string operations

Keep practicing! Write small programs to get comfortable with these concepts. Python is all about simplicity and readability!