Core Python Programming (2nd Edition)

'abc' > 'xyz'
False
>>> 'abc' < 'xyz'
True
>>> [3, 'abc'] == ['abc', 3]
False
>>> [3, 'abc'] == [3, 'abc']
True
Also, unlike many other languages, multiple comparisons can be made on the same line, evaluated in
left-to-right order:
>>> 3 < 4 < 7 # same as ( 3 < 4 ) and ( 4 < 7 )
True
>>> 4 > 3 == 3 # same as ( 4 > 3 ) and ( 3 == 3 )
True
>>> 4 < 3 < 5 != 2 < 7
False
We would like to note here that comparisons are strictly between object values, meaning that the
comparisons are between the data values and not the actual data objects themselves. For the latter, we
will defer to the object identity comparison operators described next.
4.5.2. Object Identity Comparison
In addition to value comparisons, Python also supports the notion of directly comparing objects
themselves. Objects can be assigned to other variables (by reference). Because each variable points to
the same (shared) data object, any change effected through one variable will change the object and
hence be reflected through all references to the same object.
In order to understand this, you will have to think of variables as linking to objects now and be less
concerned with the values themselves. Let us take a look at three examples.
Example 1: foo1 and foo2 reference the same object
foo1 = foo2 = 4.3
When you look at this statement from the value point of view, it appears that you are performing a
multiple assignment and assigning the numeric value of 4.3 to both the foo1 and foo2 variables. This is
true to a certain degree, but upon lifting the covers, you will find that a numeric object with the contents
or value of 4.3 has been created. Then that object's reference is assigned to both foo1 and foo2,
resulting in both foo1 and foo2 aliased to the same object. Figure 4-1 shows an object with two
references.
Figure 4-1. foo1 and foo2 reference the same object