repr 的输出什么时候有用？
我一直在阅读有关 Python 中的 repr 的内容。我想知道 repr 的输出的应用是什么。例如
class A:
pass
repr(A) ='<class __main__.A at 0x6f570>'
b=A()
repr(b) = '<__main__.A instance at 0x74d78>'
，人们什么时候会对'或'<__main__.A instance at 0x74d78>'感兴趣？
I have been reading about repr in Python. I was wondering what the application of the output of repr is. e.g.
class A:
pass
repr(A) ='<class __main__.A at 0x6f570>'
b=A()
repr(b) = '<__main__.A instance at 0x74d78>'
When would one be interested in '<class __main__.A at 0x6f570>' or'<__main__.A instance at 0x74d78>'?
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理论上，repr(obj) 应该输出一个字符串，以便可以将其输入到 eval 中以重新创建对象。换句话说，
应该重现该对象。
实际上，
repr通常是str的“精简”版本。str可能会打印对象的人类可读形式，而repr则打印出对象的类等信息，通常用于调试目的。但有用性在很大程度上取决于您的情况以及相关对象如何处理repr。Theoretically,
repr(obj)should spit out a string such that it can be fed intoevalto recreate the object. In other words,should reproduce the object.
In practice,
repris often a "lite" version ofstr.strmight print a human-readable form of the object, whereasreprprints out information like the object's class, usually for debugging purposes. But the usefulness depends a lot on your situation and how the object in question handlesrepr.有时您必须处理或呈现一个字节字符串，例如
如果您打印你得到的这个（在 Ubuntu 中）
Sometimes you have to deal with or present a byte string such as
If you print this out (in Ubuntu) you get
which is not very helpful to others trying to understand your byte string. In the comments, John points out that in Windows,
print(bob2)results in something likebobð¤¢. The problem is that Python detects the default encoding of your terminal/console and tries to decode the byte string according to that encoding. Since Ubuntu and Windows uses different default encodings (possiblyutf-8andcp1252respectively), different results ensue.In contrast, the repr of a string is unambiguous:
When people post questions here on SO about Python strings, they are often asked to show the repr of the string so we know for sure what string they are dealing with.
In general, the repr should be an unambiguous string representation of the object.
repr(obj)calls the objectobj's__repr__method. Since in your example the classAdoes not have its own__repr__method,repr(b)resorts to indicating the class and memory address.You can override the
__repr__method to give more relevant information.In your example,
'<__main__.A instance at 0x74d78>'tells us two useful things:bis an instance of classAin the
__main__namespace,
memory at address 0x74d78.
You might for instance, have two instances of class
A. If they have the same memory address then you'd know they are "pointing" to the same underlying object. (Note this information can also be obtained usingid).repr()的主要用途是在交互式解释器和调试器中使用它以人类可读的形式格式化对象。您给出的示例主要用于调试目的。The main purpose of
repr()is that it is used in the interactive interpreter and in the debugger to format objects in human-readable form. The example you gave is mainly useful for debugging purposes.