A Comprehensive Guide to Python’s __contains__ and __iter__ Magic Methods: Exploring Iteration and Membership in Python – KDnuggets

Python is a versatile and powerful programming language that offers a wide range of features and functionalities. One of the key aspects of Python is its support for object-oriented programming, which allows developers to create reusable and modular code. In this article, we will explore two important magic methods in Python – __contains__ and __iter__ – that are used to implement iteration and membership testing in Python.

The __contains__ method is used to implement the in operator in Python, which is used to test for membership in a sequence. When the in operator is used with an object, Python calls the object’s __contains__ method to determine if the object contains the specified value. The __contains__ method should return True if the value is present in the object, and False otherwise.

Here is an example of how the __contains__ method can be implemented in a custom class:

“`python
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
“`

In this example, the __contains__ method checks if the specified value is present in the list stored in the MyList object.

The __iter__ method is used to implement iteration over an object in Python. When an object is passed to the iter() function, Python calls the object’s __iter__ method to obtain an iterator for the object. The iterator can then be used to iterate over the elements of the object using a for loop or by calling the next() function.

Here is an example of how the __iter__ method can be implemented in a custom class:

“`python
class MyRange:
def __init__(self, start, end):
self.start = start
self.end = end

def __iter__(self):
return self

def __next__(self):
if self.start >= self.end:
raise StopIteration
result = self.start
self.start += 1
return result

my_range = MyRange(1, 5)
for num in my_range:
print(num) # Output: 1 2 3 4
“`

In this example, the MyRange class implements both the __iter__ and __next__ methods to create an iterator that generates a sequence of numbers from start to end.

By implementing the __contains__ and __iter__ magic methods in custom classes, developers can add support for membership testing and iteration to their objects. These magic methods provide a powerful way to customize the behavior of objects in Python and make them more versatile and flexible.

• Source Link: https://zephyrnet.com/understanding-pythons-iteration-and-membership-a-guide-to-__contains__-and-__iter__-magic-methods-kdnuggets/