Learning Python for Forensics

ValueError

ValueError, unlike TypeError, occurs not because the data type is incorrect, but because the value is incorrect. For example, when we attempt to divide a list by a number we receive a TypeError because a list is the wrong type for division. A list, however, is the right type to support multiple variable assignment but needs the correct number of values to unpack:

>>> x, y, z = [1, 2]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: need more than 2 values to unpack
>>> x, y = [1, 2, 3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many values to unpack
>>> x, y, z = [1, 2, 3]
>>> print x, y, z
1 2 3