Nội dung chính
- The need for __str__ method:
- How to call __str__ method
- 1. Default implementation
- 2. Custom __str__ method
- 3. __repr__ method defined only
- Introduction to the Python __str__ method
- What is the purpose of str [] method?
- What is the purpose of defining the functions __ str __ and __ repr __ within a class how are the two functions different?
- What is __ str __ in Django?
- What does str [] do in Python example?
The need for __str__ method:
The __str__ method in Python represents the class objects as a string – it can be used for
classes. The __str__ method should be defined in a way that is easy to read and outputs all the members of the class. This method is also used as a debugging tool when the members of a class need to be checked.
The __str__ method is called when the following functions are invoked on the object and return a string:
- print[]
- str[]
If we have not defined the __str__, then it will call the __repr__ method. The __repr__ method returns a string
that describes the pointer of the object by default [if the programmer does not define it].
How to call __str__ method
1. Default implementation
class MyClass:
x = 0
y = ""
def __init__[self, anyNumber, anyString]:
self.x = anyNumber
self.y = anyString
myObject = MyClass[12345, "Hello"]
print[myObject.__str__[]]
print[myObject.__repr__[]]
print[myObject]
The above code shows an example where neither __str__ nor __repr__ are defined. Calling __str__ calls the default __repr__ method, and they all give the same output, the pointer of our object.
2. Custom __str__ method
class MyClass:
x = 0
y = ""
def __init__[self, anyNumber, anyString]:
self.x = anyNumber
self.y = anyString
def __str__ [self]:
return 'MyClass[x=' + str[self.x] + ' ,y=' + self.y + ']'
myObject = MyClass[12345, "Hello"]
print[myObject.__str__[]]
print[myObject]
print[str[myObject]]
print[myObject.__repr__[]]
The
code above shows the output once you have defined the __str__ method. When __str__, print[], or str[] are called you will get your defined output. Make note that the __repr__ output remains the same.
3. __repr__ method defined only
class MyClass:
x = 0
y = ""
def __init__[self, anyNumber, anyString]:
self.x = anyNumber
self.y = anyString
def __repr__ [self]:
return 'MyClass[x=' + str[self.x] + ' ,y=' + self.y + ']'
myObject = MyClass[12345, "Hello"]
print[myObject.__str__[]]
print[myObject]
print[str[myObject]]
print[myObject.__repr__[]]In the first example we saw that when __str__ is not defined it automatically calls the __repr__ method. Therefore, the output of all the functions - __str__, str[], and __repr__ - are the same. Moreover,
the __repr__ method does not necessarily need to return a string. In case it does not return a string, the print[] statements will throw an error.
CONTRIBUTOR
Shahpar Khan
Copyright ©2022 Educative, Inc. All rights reserved
Summary: in this tutorial, you’ll learn how to use the Python __str__ method to make a string representation of a class.
Introduction to the Python __str__ method
Let’s start with the Person class:
Code language: Python [python]
class Person: def __init__[self, first_name, last_name, age]: self.first_name = first_name self.last_name = last_name self.age = age
The Person class has three instance attributes including first_name, last_name, and age.
The following creates a new instance of the Person class and display it:
person = Person['John', 'Doe', 25] print[person]Code language: Python [python]
Output:
Code language: Python [python]
When you use the print[] function to display the instance of the Person class, the print[] function shows the memory address of that instance.
Sometimes, it’s useful to have a string representation of an instance of a
class. To customize the string representation of a class instance, the class needs to implement the __str__ magic method.
Internally, Python will call the __str__ method automatically when an instance calls the str[] method.
Note that the print[] function converts all non-keyword arguments to strings by passing them to the str[] before displaying the string values.
The following illustrates how to implement the __str__ method in the Person class:
Code language: Python [python]
class Person: def __init__[self, first_name, last_name, age]: self.first_name = first_name self.last_name = last_name self.age = age def __str__[self]: return f'Person[{self.first_name},{self.last_name},{self.age}]'
And
when you use the print[] function to print out an instance of the Person class, Python calls the __str__ method defined in the Person class. For example:
Code language: Python [python]
person = Person['John', 'Doe', 25] print[person]
Output:
Code language: Python [python]
Person[John,Doe,25]
Summary
- Implement the
__str__method to customize the string representation of an instance of a class.
Did you find this tutorial helpful ?
What is the purpose of str [] method?
The str[] function converts the specified value into a string.
What is the purpose of defining the functions __ str __ and __ repr __ within a class how are the two functions different?
__str__ is used in to show a string representation of your object to be read easily by others. __repr__ is used to show a string representation of the object.
What is __ str __ in Django?
str function in a django model returns a string that is exactly rendered as the display name of instances for that model.
What does str [] do in Python example?
Python str[] function returns the string version of the object. Parameters: object: The object whose string representation is to be returned. encoding: Encoding of the given object.