NameError in Python — name is not defined Fix (2026) | Tutorials Logic

# ❌ Problem
print(message)  # NameError: name 'message' is not defined

# ✅ Solution: Define the variable first
message = "Hello, World!"
print(message)

# ✅ Check for typos
username = "John"
print(username)  # Not 'userName' or 'user_name'

print(total)  # NameError!
total = 100

total = 100  # Define first
print(total)  # Then use

user_name = "Alice"
print(username)  # NameError: 'username' vs 'user_name'

firstName = "Bob"
print(firstname)  # NameError: case mismatch!

user_name = "Alice"
print(user_name)  # Exact match

firstName = "Bob"
print(firstName)  # Exact case match

# Use consistent naming convention (snake_case recommended)
user_name = "Alice"
first_name = "Bob"

def calculate():
    result = 100
    
print(result)  # NameError: result is local to calculate()

# Solution 1: Return the value
def calculate():
    result = 100
    return result
    
result = calculate()
print(result)

# Solution 2: Use global variable (not recommended)
result = 0

def calculate():
    global result
    result = 100
    
calculate()
print(result)

# Solution 3: Define outside function
result = 100

def calculate():
    print(result)  # Can read global variable
    
calculate()

result = math.sqrt(16)  # NameError: name 'math' is not defined

data = json.loads('{"key": "value"}')  # NameError!

import math
result = math.sqrt(16)

import json
data = json.loads('{"key": "value"}')

# Or import specific functions
from math import sqrt
result = sqrt(16)

from json import loads
data = loads('{"key": "value"}')

name = Alice  # NameError: name 'Alice' is not defined
print(Hello)  # NameError!

name = "Alice"  # Add quotes for strings
print("Hello")  # Strings need quotes