Core Python Programming (2nd Edition)

isinstance(c2, C2)
True
>>> isinstance(C2, c2)
Traceback (innermost last):
File "", line 1, in ?
isinstance(C2, c2)
TypeError: second argument must be a class
Note that the second argument should be a class; otherwise, you get a TypeError. The only exception is
if the second argument is a type object. This is allowed because you can also use isinstance() to check
if an object obj1 is of the type obj2, i.e.,
>>> isinstance(4, int)
True
>>> isinstance(4, str)
False
>>> isinstance('4', str)
True
If you are coming from Java, you may be aware of the warning against using its equivalent, instanceof
(), due to performance reasons. A call to Python's isinstance() will not have the same performance hit
primarily because it only needs it to perform a quick search up the class hierarchy to determine what
classes it is an instance of, and even more importantly, it is written in C!
Like issubclass(), isinstance() can also take a tuple as its second argument. This feature was added in
Python 2.2. It will return TRue if the first argument is an instance of any of the candidate types and
classes in the given tuple. Also be sure to read more about isinstance() in Section 13.16.1 on page 595.
13.12.3. hasattr(), getattr(), setattr(), delattr()
The *attr() functions can work with all kinds of objects, not just classes and instances. However, since
they are most often used with those objects, we present them here. One thing that might throw you off
is that when using these functions, you pass in the object you are working on as the first argument, but
the attribute name, the second argument to these functions, is the string name of the attribute. In other
words, when operating with obj.attr, the function call will be like *attr(obj, 'attr'...)this will be clear
in the examples that follow.
The hasattr() function is Boolean and its only purpose is to determine whether or not an object has a
particular attribute, presumably used as a check before actually trying to access that attribute. The
getattr() and setattr() functions retrieve and assign values to object attributes, respectively. getattr
() will raise an AttributeError exception if you attempt to read an object that does not have the
requested attribute, unless a third, optional default argument is given. setattr() will either add a new
attribute to the object or replace a pre-existing one. The delattr() function removes an attribute from
an object.
Here are some examples using all the *attr() BIFs: