A thorough understanding of __str__ and __repr__ in Python in one article

__str__ and __repr__What are the similarities and differences?

String representation

We all know that Python’s built-in function repr() can convert objects in the form of strings Express it so that we can identify it easily. This is the "string representation". repr() obtains the string representation of an object through the special method __repr__. If __repr__ is not implemented, when we print a vector instance to the console, the resulting string may be .

>>> class Example: pass >>> print(str(Example())) <__main__.Example object at 0x10a514f98> >>> print(repr(Example())) <__main__.Example object at 0x1088eb438> >>> >>> str(Example) "" >>> repr(Example()) '<__main__.Example object at 0x1088eb438>'

**__str__**vs.**__repr__**

Next let’s take a look at the similarities and differences between **__str__** and **__repr__**. According to the official Python documentation:

• __str__: Called by str(object) and the built-in functions format() and print() to generate an "informal" or well-formatted string representation of an object . The return value must be a string object.
• __repr__: It is called by the repr() built-in function and is used to output the "official" string representation of an object. The return value must be a string object. This method is usually used for debugging. The default implementation defined for the built-in type object calls object.__repr__().

You are confused about formal and informal formats, right? It’s okay, let’s go on to see:

1. Both can output objects

>>> x = 4 >>> repr(x) '4' >>> str(x) '4' >>> y = 'pythonic' >>> repr(y) "'pythonic'" >>> str(y) 'pythonic' >>> z = '4' >>> repr(z) "'4'" >>> str(z)# 注意，此处的输出结果形式跟str(x)一样，但x和z的类型并不一样 '4' >>> str(x) == str(z) True >>> repr(x) == repr(z) False >>> str(4) == str("4") True >>> repr(4) == repr("4") False

When x=4, when x is an integer type, the return of calling str() and repr() The result is the same,

And when y is a string type, the result of repr(y) is a "formal" string representation, while the result of str(y) is "informal" . str() allows us to understand the content of the object most quickly and is more readable.

2 .__str__ is readable, and the goal of __repr__ is clear

>>> import datetime >>> d = datetime.datetime.now() >>> str(d) '2020-04-04 20:47:46.525245' >>> repr(d) 'datetime.datetime(2020, 4, 4, 20, 47, 46, 525245)' >>>

It can be seen that repr() can better display the type, value and other information of the object, and the object description is clear of.

It is called when the str() function is used, or when an object is printed using the print function, and the string it returns is more friendly to end users.

3. Rewrite __repr__, which will also use __str_

class Student(): def __init__(self, name): self.name = name def __str__(self): return "Name：" + self.name def __repr__(self): return "姓名：" + self.name class_one = Student("Alice") print(class_one) print(str(class_one)) print(repr(class_one))

Output results:

Name：Alice Name：Alice 姓名：Alice

Summary

Common points: They are all used To output an object

Difference:

1. __str__ The target is readable, __str__() is not expected to return a valid Python expression, but can be used more conveniently or More accurate descriptive information. The goal of
2. __repr__ is clear. The returned string should be accurate, unambiguous, and express as much as possible how to create the printed object using code.
3. The use of the container’s __str__ method contains the object’s __repr__

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