Python custom class __str__ (detailed examples)

In the following article, let’s learn about what is a custom class in python. Learn what python custom classes are, and what role python custom classes can play in python programming.

When you see variable or function names in the form of __xxx__ like __slots__, you should pay attention. These have special uses in Python.

__slots__We already know how to use it, and we also know the __len__() method to allow class to act on the len() function.

In addition, there are many special-purpose functions in Python classes that can help us customize classes.

__str__

We first define a Student class and print an instance:

>>> class Student(object):
...     def __init__(self, name):
...         self.name = name
...
>>> print(Student('Michael'))
<__main__.Student object at 0x109afb190>

Print out a bunch of <__main__.Student object at 0x109afb190>, which looks quite ugly.

How can I print it beautifully? You only need to define the __str__() method and return a good-looking string:

>>> class Student(object):
...     def __init__(self, name):
...         self.name = name
...     def __str__(self):
...         return 'Student object (name: %s)' % self.name
...
>>> print(Student('Michael'))
Student object (name: Michael)

The instance printed out in this way not only looks good, but also makes it easy to see the important data inside the instance.

But careful friends will find that directly typing the variable without printing, the printed example still does not look good:

>>> s = Student('Michael')
>>> s<__main__.Student object at 0x109afb310>

This is because the direct display of the variable call is not __str__(), but _ _repr__(), the difference between the two is that __str__() returns the string seen by the user, while __repr__() returns the string seen by the program developer. In other words, __repr__() is for debugging.

The solution is to define another __repr__(). But usually the codes of __str__() and __repr__() are the same, so there is a lazy way of writing:

class Student(object):
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return 'Student object (name=%s)' % self.name
    __repr__ = __str__

The above is all the content described in this article, this article mainly introducesPython custom class__str__ related knowledge, I hope you can use the information to understand the above content. I hope what I have described in this article will be helpful to you and make it easier for you to learn python.

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