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<h3>Object Identity and Type</h3>
<p>The built-in function <tT CLAss="monofont">id()</tt> returns the identity of an object as an integer. This integer usually corresponds to the object抯 location in memory, although this is specific to the implementation. The <TT CLass="monofont">is</tT>  operator compares the identity of two objects. The built-in function <TT Class="monofont">type()</tt> returns the type of an object. For example:</p>

<pre>

# Compare two objects 
def compare(a,b): 
    print 'The identity of a is ', id(a) 
    print 'The identity of b is ', id(b) 
    if a is b: 
        print 'a and b are the same object' 
    if a == b: 
        print 'a and b have the same value' 
    if type(a) is type(b): 
        print 'a and b have the same type' </pre>

<p>The type of an object is itself an object. This type object is uniquely defined and is always the same for all instances of a given type. Therefore, the type can be compared using the <tt clasS="monofont">is</tt>  operator. The standard module <Tt clAss="monofont">types</tt>  contains the type objects for all the built-in types and can be used to perform type-checking. For example:</P>

<pre>

import types 
if type(s) is types.ListType: 
    print 'Is a list' 
else: 
    print 'Is not a list' </PRE>

<P>When comparing object types in which user-defined classes are involved, it may be better to use the <tt clASS="monofont">isinstance()</Tt> function as described in <a hrEF="72.html">Chapter 7</A>, 揅lasses and Object-Oriented Programming.
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