re 模块错误 error: bad character range

简介: 下午,看到堆栈的内容。于是上机实验了一番 >>> bds = '10+6/5-4*2' # 数学运算表达式   想用 findall 把运算符号提取出来 >>> import re >>> m = re.

 

下午,看到堆栈的内容。于是上机实验了一番

>>> bds = '10+6/5-4*2' # 数学运算表达式

 

想用 findall 把运算符号提取出来

>>> import re
>>> m = re.findall(r'[+-*/]', bds) # 习惯性地按加减乘除顺序排列:'[+-*/]'

 

可是报错: bad character range

>>> 
... ... 
... ... error: bad character range

错误的字符域?这是什么鬼?会不会跟字符排列顺序有关?

 

好吧,先看看这四个字符的 ascii 码:

>>> print([ord(x) for x in '+-*/'])
 [43, 45, 42, 47]

哦,其中星号 '*' 的码值 42 最小。

 

死马当活马医,把原来的 '+-*/' 按码值调整为 '*+-/' ,看看又如何:

>>> m = re.findall(r'[*+-/]', bds) # 按ASCII码值调整顺序为:'[*+-/]'
>>> m
 ['+', '/', '-', '*']

哇,终于搞定!!

 

总结:

一个猜想:re模块搜查单字符,其字符集合必须按其ASCII值(或者说编码值)由小到大排列,否则报错: error: bad character range

 

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