2.1.3 Comparisons

















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2.1.3 Comparisons



Comparison operations are supported by all objects. They all have the
same priority (which is higher than that of the Boolean operations).
Comparisons can be chained arbitrarily; for example, x <
y <= z is equivalent to x < y and
y <= z, except that y is evaluated only once (but
in both cases z is not evaluated at all when x <
y is found to be false).



This table summarizes the comparison operations:





Operation 
Meaning 
Notes 


<
strictly less than
 
<=
less than or equal
 
>
strictly greater than
 
>=
greater than or equal
 
==
equal
 
!=
not equal
(1)
<>
not equal
(1)
is
object identity
 
is not
negated object identity
 




Notes:



(1)
<> and != are alternate spellings for the same operator.
(I couldn't choose between ABC and C! :-)

!= is the preferred spelling; <> is obsolescent.






Objects of different types, except different numeric types, never
compare equal; such objects are ordered consistently but arbitrarily
(so that sorting a heterogeneous array yields a consistent result).
Furthermore, some types (for example, file objects) support only a
degenerate notion of comparison where any two objects of that type are
unequal. Again, such objects are ordered arbitrarily but
consistently.



Instances of a class normally compare as non-equal unless the class
defines the __cmp__() method. Refer to the
Python Reference Manual for
information on the use of this method to effect object comparisons.


Implementation note: Objects of different types except
numbers are ordered by their type names; objects of the same types
that don't support proper comparison are ordered by their address.


Two more operations with the same syntactic priority,
"in" and "not in", are supported
only by sequence types (below).








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