Python 中的 !r 和 %r 有什么区别？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/33097143/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
What is the difference between !r and %r in Python?
提问by b_pcakes
As the title states, what is the difference between these two flags? It seems they both convert the value to a string using repr()? Also, in this line of code:
正如标题所述，这两个标志有什么区别？似乎他们都使用 repr() 将值转换为字符串？此外，在这行代码中：
"{0!r:20}".format("Hello")
What does the 0 in front of the !r do?
!r 前面的 0 有什么作用？
采纳答案by Martijn Pieters
%ris not a valid placeholder in the str.format()formatting operations; it only works in old-style %string formatting. It indeed converts the object to a representation through the repr()function.
%r不是str.format()格式化操作中的有效占位符；它仅适用于旧式%字符串格式。它确实通过repr()函数将对象转换为表示。
In str.format(), !ris the equivalent, but this also means that you can now use all the format codesfor a string. Normally str.format()will call the object.__format__()method on the object itself, but by using !r, repr(object).__format__()is used instead.
In str.format(),!r是等价的，但这也意味着您现在可以使用字符串的所有格式代码。通常str.format()会object.__format__()在对象本身上调用该方法，但通过使用!r,repr(object).__format__()改为使用。
There are also the !sand (in Python 3) !aconverters; these apply the str()and ascii()functions first.
还有!s和（在 Python 3 中）!a转换器；这些首先应用str()和ascii()功能。
The 0in front indicates what argument to the str.format()method will be used to fill that slot; positional argument 0is "Hello"in your case. You could use namedarguments too, and pass in objects as keyword arguments:
在0前面指示什么参数的str.format()方法将被用于填充该插槽; 位置参数0是"Hello"在您的案件。您也可以使用命名参数，并将对象作为关键字参数传入：
"{greeting!r:20}".format(greeting="Hello")
Unless you are using Python 2.6, you can omit this as slots without indices or names are automatically numbered; the first {}is 0, the second {}takes the second argument at index 1, etc.
除非您使用的是 Python 2.6，否则您可以省略它，因为没有索引或名称的插槽会自动编号；第一个{}是0，第二{}个在 index 处采用第二个参数，依此类推1。
