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Equality vs Identity vs Membership Operation in Python

Indhumathy

ARTICLE SUMMARY

Indhumathy shares with us her approach on Equality vs Identity vs Membership Operation in Python. An insightful post on her view to an equality comparison.

Equality vs Identity vs Membership Operation

In python, we might have seen isin , == in python.
is is used for identity comparison
in is used for membership operations.
== is used for equality comparison.

Let’s learn more about this in this article.

Equality Comparison(== )

Equality Comparison is done by == operator. It compares the value of two objects.

Sequences (instances of tuple, list, or range) can be compared only within each of their types. Equality comparison across these types results in inequality.

#listn1=[1,2,3]n2=[1,2,3]print (n1==n2)#Output:True#tuplet1=(1,2,3)t2=(1,2,3)print (t1==t2)#Output:True#range objectr1=range(5)r2=range(5)print (r1==r2)#Output:True#Comparing tuple and listprint (n1==t1)#Output:False

Mappings (instances of dict) compare equal if and only if they have equal (key, value) pairs.

d1={'a':1,'b':2}d2={'a':1,'b':2}print (d1==d2)#Output:True

Equality Comparison on string and int objects. They compare equal if their values are the same.

s="hello"s1="hello"s2="Hello"print (s==s1)#Output:Trueprint (s1==s2)#Output:Falsea=10b=10print (a==b)#Output:True

Identity Comparison (is)

Identity Comparison is done by using is and is not operator.

x is y →True if and only x and y are the same object.x is not y →True if x and y are not the same object

An Object’s identity is determined using the id() function. This is the address of the object in memory.

Identical objects will always compare equal.
x is y implies x == y

Lightbulbs, Python concept

Example 1:Testing is operator in immutable objects like int, strings, tuple.

Immutable data types:

For immutable datatype, operations that compute new values may actually return a reference to any existing object with the same type and value.

Ex. a = 1; b = 1a and b may or may not refer to the same object with the value one, depending on the implementation

#inta=10b=10print (id(a))#Output:2047928384print (id(b))#Output:2047928384print (a is b)#Output:True#stringa="hello"b="hello"print (id(a))#Output:42785376print (id(b))#Output:42785376print (a is b)#Output:True#tuplea=(1,2,3)b=(1,2,3)print (id(a))print (id(b))print ( a is b)

Example 2:

Testing is operator in mutable objects like a list.

Mutable data types:

c = []; d = []
c and d are guaranteed to refer to two different, unique, newly created empty lists.

a=[1,2,3]b=[1,2,3]print (id(a))#Output:13056008print (id(b))#Output:13190696print ( a is b)#Output:False

As per PEP 8

Comparisons to singletons like None should always be done with is or is not, never the equality operators. Therefore, always be aware of writing if x when you really mean if x is not None.
When testing, if the variable or argument that defaults to None was set to some other value – you will need to determine whether the other value might have a type (such as a container). As that could be false in a boolean context!

Membership Operation(in)

Membership Operation is done by using in and not in operator.

x in s →Returns True if x is a member of s, False otherwise.x not in s →Returns True if x is not a member of s, False otherwise.

All built-in sequences, set types,dict, strings, byte types support membership operation

Strings:

x in y → True if an only x is a substring of y

Example 1:
s1="hello"print ("h" in s1)#Output:Trueprint ("e" not in s1)#Output:False

2:

s1="hello"print (h in s1)#Output:NameError: name 'h' is not defined

3:

Empty strings are always considered as a substring of any other strings.

s1="hello"print ("" in s1)#Output:True

2. Sequences Types(List,tuple,range object)

#listn1=[1,2,3]print (1 in n1)#Output:Trueprint (2 not in n1)#Output:False#tuplet1=(1,2,3)print (1 in t1)#Output:Trueprint (2 not in t1)#Output:False#ranger1=range(5)print (1 in r1)#Output:Trueprint (2 not in r1)#Output:False

3.Set types (set,frozenset)

#sets1={1,2,3}print (1 in s1)#Output:Trueprint (2 not in s1)#Output:False#frozensets2=frozenset({1,2,3})print (1 in s2)#Output:Trueprint (2 not in s2)#Output:False

4.Dictionary

in operator will check whether the dictionary has a given key.

1:

In the below example, 1 in d1 returns False, because in will test only dictionary keys.

d1={'a':1,'b':2,'c':3}print ( 1 in d1)#Output:False

2:

If we mention d.values(), in operator will test in dictionary values.

d={'a':1,'b':2,'c':3}print ( 1 in d.values())#Output:True

3:

If we mention d.items(),in operator will test for the key, value pairs

d1={‘a’:1,’b’:2,’c’:3}print ( 1 in d1.items())#Output:Falseprint ((‘a’,1) in d1.items())#Output:True

Python coding

Equality vs Identity vs Membership Operation

1.Syntax and functions used for these operations

2.Return type is Boolean for all these operations

Resources (Python Documentation)

Operators

Comparison Operator

Membership Operation

comparisons

PEP 8

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