python中str（）和repr（）的区别

 >>> s = 'Hello, world.'
 >>> str(s)
 'Hello, world.'
 >>> repr(s)
 "'Hello, world.'"
 >>> str(1.0/7.0)
 '0.142857142857'
 >>> repr(1.0/7.0)
 '0.14285714285714285'
 >>> x = 10 * 3.25
 >>> y = 200 * 200
 >>> s = 'The value of x is ' + repr(x) + ', and y is ' + repr(y) + '...'
 >>> print s
 The value of x is 32.5, and y is 40000...
 >>> # The repr() of a string adds string quotes and backslashes:
 ... hello = 'hello, world\n'
 >>> hellos = repr(hello)
 >>> print hellos
 'hello, world\n'
 >>> # The argument to repr() may be any Python object:
 ... repr((x, y, ('spam', 'eggs')))
 "(32.5, 40000, ('spam', 'eggs'))"

一种是通过str函数，他会把值转换为合理形式的字符串，以便用户可以理解；另一种是通过repr函数，她会创建一个字符串，以合法的Python表达式的形式来表示值。

repr也可以做``反引号的实现。如果希望答应一个包含数字的句子，那么反引号就很有用了。比如：

 >>> temp = 100
 >>> print 'hello' + temp

 Traceback (most recent call last):
   File "<pyshell#1>", line 1, in <module>
     print 'hello' + temp
 TypeError: cannot concatenate 'str' and 'int' objects
 >>> print 'hello'+`temp`
 hello100