Is raised when you tried to use a variable, method or function that is not initialized (at least not before). In other words, it is raised when a requested local or global name is not found. It's possible that you misspelt the name of the object or forgot to
import something. Also maybe it's in another scope. We'll cover those with separate examples.
It's possible that you forgot to initialize it, specially if it is a constant
foo # This variable is not defined bar() # This function is not defined
baz() def baz(): pass
#needs import math def sqrt(): x = float(input("Value: ")) return math.sqrt(x)
The so-called LEGB Rule talks about the Python scopes. It's name is based on the different scopes, ordered by the correspondent priorities:
Local → Enclosed → Global → Built-in.
As an example:
for i in range(4): d = i * 2 print(d)
d is accesible because the
for loop does not mark a new scope, but if it did, we would have an error and its behavior would be similar to:
def noaccess(): for i in range(4): d = i * 2 noaccess() print(d)
NameError: name 'd' is not defined