Python NameError: Name is Not Defined

Python is a powerful programming language. But errors can occur. One common error is the NameError: name is not defined. This error happens when Python cannot find a name in your code.

What is a NameError?

A NameError occurs when Python tries to use a variable or function that hasn't been defined yet. This can happen for several reasons. For example, you might have misspelled a variable name or forgotten to define it.

Understanding why this error occurs is crucial. For more details, check out our article on Why Does NameError Occur in Python?.

Common Causes of NameError

There are several common causes of the NameError. Let's look at a few examples.

Misspelled Variable Name

One common cause is misspelling a variable name. Python is case-sensitive. So, myVar and myvar are different.

# Example of a misspelled variable
myVar = 10
print(myvar)  # This will raise a NameError

NameError: name 'myvar' is not defined

Using a Variable Before Definition

Another cause is using a variable before it is defined. Python reads code from top to bottom. So, if you try to use a variable before defining it, you'll get a NameError.

# Example of using a variable before definition
print(myVar)  # This will raise a NameError
myVar = 10

NameError: name 'myVar' is not defined

Scope Issues

Scope issues can also cause a NameError. Variables defined inside a function are local to that function. If you try to use them outside, you'll get a NameError.

# Example of scope issue
def myFunction():
    localVar = 5

print(localVar)  # This will raise a NameError

NameError: name 'localVar' is not defined

How to Fix NameError

Fixing a NameError is usually straightforward. Here are some tips to help you resolve it.

Check for Typos

First, check for typos in your variable names. Make sure you are using the correct case and spelling.

Define Variables Before Use

Ensure that all variables are defined before you use them. Python reads code from top to bottom. So, define your variables at the beginning of your script or function.

Understand Scope

Understand the scope of your variables. If you define a variable inside a function, it is local to that function. To use it outside, you need to return it or define it globally.

For more detailed solutions, visit our guide on How to Fix NameError in Python.

Example: Fixing a NameError

Let's look at an example of how to fix a NameError.

# Incorrect code
print(myVar)  # This will raise a NameError
myVar = 10

# Corrected code
myVar = 10
print(myVar)  # This will work

10

Conclusion

The NameError: name is not defined is a common error in Python. It usually occurs due to typos, undefined variables, or scope issues. By understanding these causes, you can easily fix the error.

For a deeper understanding, read our article on Understanding NameError in Python.

Remember, debugging is a key skill in programming. With practice, you'll get better at identifying and fixing errors like the NameError.