What is the difference between NameError and AttributeError in Python?

Question

What is the diffference between those 2 types of errors? When to use each one of them?

Answer 1

Attributes are properties of functions or classes or modules, and if a property is not found then it raises attribute error.

NameError are related to variables.

>>> x=2
>>> y=3
>>> z    #z is not defined so NameError

Traceback (most recent call last):
  File "<pyshell#136>", line 1, in <module>
    z
NameError: name 'z' is not defined

>>> def f():pass

>>> f.x=2 #define an attribue of f
>>> f.x
2
>>> f.y   #f has no attribute named y

Traceback (most recent call last):
  File "<pyshell#141>", line 1, in <module>
    f.y
AttributeError: 'function' object has no attribute 'y'

>>> import math   #a module  

>>> math.sin(90) #sin() is an attribute of math
0.8939966636005579

>>> math.cosx(90)  #but cosx() is not an attribute of math

Traceback (most recent call last):
  File "<pyshell#145>", line 1, in <module>
    math.cosx(90)
AttributeError: 'module' object has no attribute 'cosx'

Answer 2

From the docs I think the text is pretty self explanatory.

NameError Raised when a local or global name is not found. This applies only to unqualified names. The associated value is an error message that includes the name that could not be found.

AttributeError Raised when an attribute reference (see Attribute references) or assignment fails. (When an object does not support attribute references or attribute assignments at all, TypeError is raised.)

In you example above the reference to z raises NameError as you are trying to access an unqualified name (either local or global)

In you last example math.cosx is a dotted access (attribute reference) in this case is an attribute of the math module and thus AttributeError is raised.