How to Fix NameError: name is not defined in Python Causes & Solutions

 

 What Is This Error?

The error NameError: name 'x' is not defined occurs when you try to use a variable before declaring or assigning it.

 Example:

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

 Common Causes and How to Fix Them

1.  Variable Not Declared Yet

x = 10
print(x)  #  Works

Fix: Always make sure the variable is assigned before it’s used.

2.  Variable Inside Function Scope Only

def greet():
    name = "Alice"

print(name)  #  NameError

Fix: Use the variable inside its scope:

def greet():
    name = "Alice"
    print(name)

greet()

3.  Misspelled Variable Name

count = 5
print(coutn)  #  NameError

Fix: Double-check spelling – IDEs or linters can help.

4.  Using Global Variable Without Declaration

x = 5

def update():
    x += 1  #  UnboundLocalError

update()

Fix: Declare global if modifying global variable:

x = 5

def update():
    global x
    x += 1

update()

5.  Using Variable Before Assignment

def show():
    print(msg)  #  NameError
    msg = "Hello"

show()

Fix: Move assignment before usage, or pass as an argument.

6.  Using if or try Without Initialization

if False:
    result = "Done"

print(result)  #  NameError

Fix: Initialize variable outside the condition:

result = None
if False:
    result = "Done"
print(result)  #  None

 Best Practices

• Always initialize variables before use
• Use clear and consistent variable names
• Consider linters like Flake8, Pylint, or MyPy
• Test your functions independently
• Handle NameError in large scripts using try-except blocks

 Summary

Cause	Fix
Variable used before defined	Define the variable first
Scope error inside functions	Use global or pass as argument
Misspelled variable name	Fix the typo
Condition or loop not triggered	Initialize variable beforehand