Scientific Computing with Python 3

Type checking

The direct way to see the type of a variable is to use the type command:

label = 'local error'
type(label) # returns str
x = [1, 2] # list
type(x) # returns list

However, if you want to test for a variable to be of a certain type, you should use isinstance (instead of comparing the types with type):

isinstance(x, list) # True

The reason for using isinstance becomes apparent after having read Chapter 8, Classes, and in particular the concept of subclassing and inheritance in section Subclassing and Inheritance in Chapter 8, Classes. In short, often different types share some common properties with some basic type. The classical example is the type bool, which is derived by subclassing from the more general type int. In this situation, ...