September 19, 2026

NameError: name 'x' is not defined — The Most Common Causes

NameError: name 'x' is not defined is one of the first errors most people hit, and it almost always comes down to one of three specific mistakes — not a mysterious Python quirk.

Cause #1: a typo in the variable name

mesage = "Hello"
print(message)

Traceback (most recent call last):
  File "script.py", line 2, in <module>
    print(message)
NameError: name 'message' is not defined

mesage and message are two different names as far as Python is concerned — a single missing letter is enough. This is the most common cause by far, and the fix is just careful reading (or an editor with autocomplete, which would have caught this immediately).

Cause #2: using a variable before it's defined

print(count)
count = 5

Traceback (most recent call last):
  File "script.py", line 1, in <module>
    print(count)
NameError: name 'count' is not defined

Python runs your file top to bottom, one line at a time. count doesn't exist yet when print(count) runs, even though it gets created one line later — order matters.

Cause #3: a variable defined inside a function, used outside it

def set_name():
    name = "Ava"

set_name()
print(name)

Traceback (most recent call last):
  File "script.py", line 5, in <module>
    print(name)
NameError: name 'name' is not defined

Variables created inside a function only exist inside that function — this is called local scope. Calling set_name() runs the function and then throws its local name variable away; nothing outside the function ever sees it, even though the function clearly ran.

For more on how variables and scope work in Python, see the Variables and Data Types lesson in our free Python course.