艰难地学习 Python，练习 10.4
#Combine %r with double-quote and single-quote escapes and print them out.
#Compare %r with %s. Notice how %r prints it the way you'd write it in your file,
#but %s prints it the way you'd like to see it?
这是我为练习编写的内容：
1) mybugs1 = "Guido said: %r and moved on." %'I \'love\' \"my\" bugs'
2) mybugs2 = "Stallman said: %s and moved on." % 'I \'love\' \"my\" bugs'
3) print mybugs1
4) print mybugs2
输出
Guido said: 'I \'love\' "my" bugs' and moved on.
Stallman said: I 'love' "my" bugs and moved on.
问题
%r 不会按照我在 .py 文件中编写的方式打印所有内容（例如，它在第 1 行打印“my”而不是“my”）。为什么？
#Combine %r with double-quote and single-quote escapes and print them out.
#Compare %r with %s. Notice how %r prints it the way you'd write it in your file,
#but %s prints it the way you'd like to see it?
This is what I wrote for the exercise:
1) mybugs1 = "Guido said: %r and moved on." %'I \'love\' \"my\" bugs'
2) mybugs2 = "Stallman said: %s and moved on." % 'I \'love\' \"my\" bugs'
3) print mybugs1
4) print mybugs2
Output
Guido said: 'I \'love\' "my" bugs' and moved on.
Stallman said: I 'love' "my" bugs and moved on.
Question
%r doesn't print everything the way I'd write it in my .py file (for example it prints "my" instead of \"my\" at line 1). Why?
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在 python 中编写字符串文字的方法有多种，包括单引号或双引号、单行或多行、原始或普通。不过，这些都没有保留在字符串本身中；一旦解析器解析它，就不会保留有关它如何在源代码中呈现的信息；它甚至不需要在源代码中，您可以动态生成字符串，例如通过从文件中读取字符串、询问用户或将数字转换为字符串。
因此，当您
repr()一个字符串时，Python猜测采用哪种方式将其格式化为看起来像文字。它使用的规则很简单，如果字符串包含单引号但不包含双引号，则使用单行、双引号、非原始文字；在所有其他情况下，它使用单行、单引号、非原始文字；换句话说，Python 更喜欢单引号，但如果它格式化的字符串包含单引号，但没有双引号，它可以通过使用双引号字符串来repr()该字符串，而无需反斜杠转义引号。请记住，
repr()不会返回您输入的内容，因为它不知道您输入的内容；您可能永远不会全部输入。它返回一些可以解析回相同值的东西。身份*是：不是
*
repr()对此也不神奇，并非所有对象都以这样的方式实现__repr__保留了这个约束。 repr 主要用于提供有用的调试信息，而不是用于生成 python 代码there are several ways to write string literals in python, with single or double quotes, single-line or multiline, raw or normal. None of that is preserved in the string itself, though; once the parser parses it, no information remains about how it was presented in the source; it doesn't even need to be in the source, you could generate the string dynamically, say, by reading it from a file, asking the user, or turning a number into a string.
So when you
repr()a string, python guesses which way to format it to look like a literal. The rules it uses are simple, if the string contains single quotes but no double quotes, it uses a single-line, double-quote, non-raw literal; In all other cases, it uses a single-line, single-quote, non-raw literal; Stated another way, python prefers single quotes, but if it's formatting a string that has single quotes, but not double quotes, it canrepr()that string without backslash escaping the quotes by using a double quoted string.remember,
repr()doesn't return what you typed, because it doesn't know what you typed; you might never have typed it all. It returns something that can be parsed back into the same value. The identity* is:not
*
repr()is not magical for this either, not all objects implement__repr__in a way that preserves this constraint. repr is mostly used for providing useful debugging information, not for generating python code单引号内的双引号不必转义，反之亦然。
解析器删除反斜杠。
例子
Double-quotes inside single-quotes don't have to be escaped, and vice versa.
The parser removes the backslash.
Example