What is __contains__() in Python?

__contains__() is a special method in Python that allows an object to define its own behavior when it is checked for containment in another object using the in keyword. The method should return True if the object contains the given value, and False otherwise.

Here's an example that demonstrates how to use __contains__():

class MyList:
    def __init__(self, values):
        self.values = values

    def __contains__(self, value):
        return value in self.values

my_list = MyList([1, 2, 3, 4, 5])

print(3 in my_list) # output: True
print(6 in my_list) # output: False

In this example, the MyList class defines its own behavior for the in keyword by implementing the __contains__() method. The method simply checks whether the given value is in the values list and returns True or False accordingly.

Note that __contains__() can be implemented for any custom object type in Python, and is often used for container types such as lists, sets, and dictionaries.

__contains__() is a special method in Python that allows objects to define custom behavior for the in operator. The in operator is used to test if a value is a member of a sequence or a collection.

When an object defines the __contains__() method, it can be used with the in operator to determine if a given value is contained within the object. The __contains__() method should return True if the value is present in the object, and False otherwise.

Here's an example of how __contains__() can be used:

class MyList:
def __init__(self, data):
self.data = data

def __contains__(self, value):
return value in self.data

my_list = MyList([1, 2, 3, 4, 5])

print(3 in my_list) # Output: True
print(6 in my_list) # Output: False