In-depth exploration of the implementation principle of len function in Python: in-depth understanding of its underlying mechanism

In-depth understanding of the len function in Python: to master its underlying implementation principles, specific code examples are required

Introduction:
Python is a concise, easy-to-read, Easy-to-learn programming language. In Python, the len() function is a very commonly used built-in function, used to return the number of elements of a container object (such as string, list, tuple, etc.). Although the len() function seems simple, a deep understanding of its underlying implementation principles is very important to improve our understanding and ability of Python. This article will introduce the underlying implementation principle of the len() function and provide specific code examples to help readers understand it in depth.

1. Basic usage of len() function
Before we start to understand the underlying implementation principle of len() function, let’s first take a look at the basic usage of len() function. The len() function can be used with any iterable object, such as strings, lists, tuples, etc.

Code example 1:

string = "Hello, World!"
print(len(string))

list1 = [1, 2, 3, 4, 5]
print(len(list1))

tuple1 = (1, 2, 3, 4, 5)
print(len(tuple1))

Output result:

13
5
5

The basic usage of the len() function is very simple: pass in an iterable object and it will return the object's The number of elements. Next, we will deeply understand the underlying implementation principle of the len() function.

2. The underlying implementation principle of the len() function
Before understanding the underlying implementation principle of the len() function, we need to clarify a concept: objects in Python are all based on the data structure of the C language. Encapsulated. The len() function is not a function provided by the Python interpreter itself, but is implemented by calling the special method __len__() of the object. This special method is called one of the object's "magic methods."

Magic methods are a set of special functions in Python that are used to overload operators or define the behavior of a class. In the len() function, it will automatically find the __len__() method of the object and call it. When we call len(object), we actually call object.__len__(), and the returned result is the result of len(object).

So, we can customize the behavior of the len() function by defining a class and implementing the __len__() method.

Code example 2:

class MyClass:
    def __len__(self):
        return 42

myObject = MyClass()
print(len(myObject))

Output result:

42

In this example, we define a class named MyClass and implement _ in this class _len__() method. When we call len(myObject), myObject.__len__() is actually called, and the return result is 42.

3. The implementation principle of len() function in different container objects
According to different container objects, the underlying implementation principle of len() function will be different. Below we will discuss the implementation principles of the len() function in strings, lists, and tuples respectively.

1. String (string)
   In Python, a string is a sequence composed of characters, so the implementation principle of the len() function is very simple, directly returning the number of characters in the string .

Code example 3:

string = "Hello, World!"
print(len(string))

Output result:

13

2. List (list)
   A list is an ordered mutable container , which can accommodate elements of any type. The elements in the list are linked through pointers, and the len() function counts and returns the number of elements by traversing these pointers.

Code example 4:

list1 = [1, 2, 3, 4, 5]
print(len(list1))

Output result:

5

3. Tuple (tuple)
   Tuple is an ordered and unavailable Variable container, similar to a list. The elements in the tuple are also linked through pointers. The len() function also counts and returns the number of elements by traversing these pointers.

Code example 5:

tuple1 = (1, 2, 3, 4, 5)
print(len(tuple1))

Output result:

5

You can see that whether it is a string, a list or a tuple, the bottom layer of the len() function The implementation principle is to count by traversing the pointer of the object.

Conclusion:
Through the in-depth understanding of the len() function in this article, we know the underlying implementation principle of the len() function and master its specific implementation in different container objects. Although the len() function is simple, understanding its underlying implementation principles is very important for improving our Python programming capabilities. In actual programming, we can customize the behavior of the len() function according to specific business needs. I hope this article will help readers deepen their understanding of the Python len() function.

Reference materials:

1. Python official documentation - Len function: https://docs.python.org/3/library/functions.html#len

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