python convert string using str & repr
可能比较 low 还是记录一下：
str 和 repr的使用过程
- str 是一个类型 （int， long 类似）， 同样她也可以作为一个工厂方法 实例一个 string
- repr 是python 内置的函数， 用于保留一个 打印值在python 代码片段里的真实状态
好,以上全是废话
>>> a = 1 >>> a + "" --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-5-ebf3ab7f3a34> in <module>() ----> 1 a + "" TypeError: unsupported operand type(s) for +: 'int' and 'str' >>> a = 1 >>> repr(a) + ""
可以看到， 我们可以通过使用 str 和 repr 来转换字符串
但是，str 只能提供一个 元string来做转换， 不可以是一个变量（她不具备执行变量的能力）
repr 是一个函数， 所以实际上是传参， 可以是变量和string
好多人都知道str()能把123数字转成字符串，python里的str()甚至还能把列表、字典等对象转成字符串。这都好理解，可是一旦把str()和repr()放在一起，大家就全都不淡定了-_-!
来看一段代码，仍是在IDLE里交互：
>>> str('hello')
'hello'
>>> repr('hello')
"'hello'"
>>> str('你好')
'\xc4\xe3\xba\xc3'
>>> repr('你好')
"'\\xc4\\xe3\\xba\\xc3'"
先看前两句：英文的'hello'在str()后仍是'hello'，可是在repr()后就变成了"'hello'"。这就说明，str()返回的就是字符串本身，而repr()虽然返回的也是字符串，但它是一个标准字符串，官方解释比较绕，我来解释下吧。repr是representation及描述的意思，不是对人的描述，而是对python机器的描述，也就是它会将某物返回一个它在python中的描述。说人话：repr(obj)告诉我们obj这个变量在背地里是什么样子，在背地里是怎么被python处理被python"玩弄"的。
在python里，我们总会被眼睛欺骗。编辑器里显示的东西，并不总是它原本的面貌。python为了方便，总是表面上一套，背地里又一套。
再来理解后两句：中文的'你好'在str()后变成了编码'\xc4\xe3\xba\xc3'，在repr()后变成了"'\xc4\xe3\xba\xc3'"。`都加上了转移符变成\，相当于把字符串中的内容都“标准化”了。至于'变成"`只是为了说明repr()返回的是一个经过处理的新字符串。
print后的str()和repr()
来看代码：
>>> print str('你好')
你好
>>> print repr('你好')
'\xc4\xe3\xba\xc3'
之前str('你好')显示的是'\xc4\xe3\xba\xc3'，而一经过print，就变成了正确的'你好'。上面说过了，命令行里直接输入一个变量，显示的是它在python后台存储的数据；而用print出来的东西，会显出出尽量友好、让人能看懂的东西。
理解了这个，对print这两个结果的不同，也就全然理解了。然后也就放弃print作为考据的心了。
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