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python 操作中常对list和字符创的转换进行操作，特此备注。

str –> list

str1 = 'abc'list1 = list(str1)list2 = str1.split()print list1            # ['a','b','c']print list2            # ['abc']str2 = 'a b c'list3 = str2.split(' ')print list3           # ['a','b','c']

list –> str

l = ['a','b','c']     #注意：l中的元素必须是字符型！str3 = ''.join(l)str4 = '.'.join(l)str5 = ' '.join(l)print str3                          # abcprint str4                           # a.b.cprint str5                          # a b cprint type(str5)

注意：l中的元素必须是字符型！

help(eval)

Evaluate the source in the context of globals and locals.    The source may be a string representing a Python expression    or a code object as returned by compile().    The globals must be a dictionary and locals can be any mapping,    defaulting to the current globals and locals.    If only globals is given, locals defaults to it.

官方文档中的解释是，将字符串str当成有效的表达式来求值并返回计算结果。globals和locals参数是可选的，如果提供了globals参数，那么它必须是dictionary类型；如果提供了locals参数，那么它可以是任意的map对象。

a = "[[1,2], [3,4], [5,6], [7,8]]"b = eval(a)print b               #[[1, 2], [3, 4], [5, 6], [7, 8]]print type(b)         # 
   
    a = "{1: 'a', 2: 'b'}"  b = eval(a)print b               #{
  1: 'a', 2: 'b'}print type(b)         #
    
     a = "([1,2], [3,4], [5,6], [7,8])"b = eval(a)print b               # ([1, 2], [3, 4], [5, 6], [7, 8])print type(b)         # 
     
    
   

实质就是

a = '1+2'b = eval(a)print b

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