There are eight comparison operations in Python. 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).
You can also give two condition and check for only one condition using or like x > y or x >= y will check for either of the two conditions. If one of the condition is true the program will proceed. This is the functionality of or .
This table summarizes the comparison operations:
| Operation | Meaning |
|---|---|
< |
strictly less than |
<= |
less than or equal to |
> |
strictly greater than |
>= |
greater than or equal to |
== |
equal to |
!= |
not equal to |
is |
object identity |
is not |
negated object identity |
Objects of different types, except different numeric types, never compare equal. Furthermore, some types (for example, function objects) support only a degenerate notion of comparison where any two objects of that type are unequal. The < , <= , > and >= operators will raise a TypeError exception when comparing a complex number with another built-in numeric type, when the objects are of different types that cannot be compared, or in other cases where there is no defined ordering.
Non-identical instances of a class normally compare as non-equal unless the class defines the __eq__() method.
Instances of a class cannot be ordered with respect to other instances of the same class, or other types of object, unless the class defines enough of the methods __lt__() , __le__() , __gt__() , and __ge__() (in general, __lt__() and __eq__() are sufficient, if you want the conventional meanings of the comparison operators).
The behavior of the is and is not operators cannot be customized; also they can be applied to any two objects and never raise an exception.
We can also chain < and > operators together. For instance, 3 < 4 < 5 will return True , but 3 < 4 > 5 will not. We can also chain the equality operator. For instance, 3 == 3 < 5 will return True but 3 == 5 < 5 will not.
Equality Comparisons - “is” vs “==”
In Python, there are two comparison operators which allow us to check to see if two objects are equal. The is operator and the == operator. However, there is a key difference between them!
The key difference between is and == can be summed up as:
-
isis used to compare identity -
==is used to compare equality
Example
First, create a list in Python.
myListA = [1,2,3]
Next, create a copy of that list.
myListB = myListA
If we use the == operator or the is operator, both will result in a True output.
>>> myListA == myListB # both lists contains similar elements
True
>>> myListB is myListA # myListB contains the same elements
True
This is because both myListA and myListB are pointing to the same list variable, which I defined at beginning of my Python program. Both lists are exactly the same, both in identity and in content.
However, what if I now create a new list?
myListC = [1,2,3]
Performing the == operator still shows that both lists are the same, in terms of content.
>>> myListA == myListC
True
However, performing the is operator will now produce a False output. This is because myListA and myListC are two different variables, despite containing the same data. Even though they look the same, they are different .
>>> myListA is myListC
False # both lists have different reference
To sum up:
- An
isexpression outputsTrueif both variables are pointing to the same reference - An
==expression outputsTrueif both variables contain the same data
However, interestingly, there are a few special cases in Python with is .
>>> a = 5
>>> b = 5
>>> a is b
True
>>> a = 1000
>>> b = 1000
>>> a is b
False
This is due to how Python is implemented. In Python, small integers (from -5 up to 256, a fast test shows) are cached. You shouldn’t rely on this detail – larger integers do not evaluate to true when you use is . For more information on this topic, view this StackOverflow thread.