🐍 Python Indentation Rules - Cheat Sheet

🎯 Golden Rules

Use 4 spaces (not tabs)
Be consistent throughout your file
Every code block must be indented
Same level = same indentation

📏 Basic Indentation Pattern

# Level 0 (no indentation)
def my_function():
    # Level 1 (4 spaces)
    if condition:
        # Level 2 (8 spaces)
        for item in list:
            # Level 3 (12 spaces)
            print("Deep inside")
        # Back to Level 2 (8 spaces)
        print("Back out one level")
    # Back to Level 1 (4 spaces)
    print("Function level")
# Back to Level 0
print("Top level")

🔧 Code Blocks That Require Indentation

Functions

def function_name():
    # Must indent here
    return "something"

If Statements

if condition:
    # Must indent here
elif other_condition:
    # Must indent here  
else:
    # Must indent here

Loops

for item in items:
    # Must indent here

while condition:
    # Must indent here

Try/Except

try:
    # Must indent here
except Exception as e:
    # Must indent here
finally:
    # Must indent here

Classes

class MyClass:
    # Must indent here
    def method(self):
        # Must indent here (8 spaces total)

❌ Common Errors

Missing Indentation

WRONG ❌

def my_function():
print("This will fail!")

CORRECT ✅

def my_function():
    print("This works!")

Inconsistent Indentation

WRONG ❌

def my_function():
    print("4 spaces")
      print("6 spaces - Error!")

CORRECT ✅

def my_function():
    print("4 spaces")
    print("4 spaces - Good!")

Missing Colon

WRONG ❌

def my_function()
    print("Missing colon above")

CORRECT ✅

def my_function():
    print("Colon added!")

🎨 Real-World Examples

Flask Route

@app.route("/endpoint", methods=["POST"])
def my_route():
    data = request.form.get("data")
    if data:
        try:
            result = process_data(data)
            return "Success", 200
        except Exception as e:
            print(f"Error: {e}")
            return "Error", 500
    else:
        return "No data", 400

Database Operations

def save_to_database(data):
    try:
        conn = psycopg2.connect(DATABASE_URL)
        cur = conn.cursor()
        cur.execute("INSERT INTO table VALUES (%s)", (data,))
        conn.commit()
        print("✅ Saved successfully")
    except Exception as e:
        print(f"❌ Database error: {e}")
    finally:
        if conn:
            conn.close()

🛠️ Debugging Tips

Check Syntax

python3 -m py_compile filename.py

Common Error Messages

IndentationError: expected an indented block
Fix: Add 4 spaces after ":"

IndentationError: unindent does not match any outer indentation level
Fix: Check your spacing is consistent

SyntaxError: invalid syntax (pointing to a line)
Fix: Check the line above for missing ":"

📐 Visual Guide

def function(): ← Colon required
    if condition: ← 4 spaces + colon
        for item: ← 8 spaces + colon
            try: ← 12 spaces + colon
                code ← 16 spaces
            except: ← 12 spaces + colon
                error ← 16 spaces
        end_for ← 8 spaces
    end_if ← 4 spaces
end_function ← 0 spaces

💡 Pro Tips

Use a good editor (VS Code, PyCharm) that shows indentation
Configure your editor to show spaces/tabs
Set tab key to insert 4 spaces
Use consistent indentation throughout entire project
When in doubt, count the spaces: 0, 4, 8, 12, 16...

🚨 Emergency Fix

If you get indentation errors:

Find the error line from the traceback
Check the line above for missing ":"
Count spaces - should be multiples of 4
Make sure all lines at same level have same spacing
Test with: python3 -m py_compile filename.py