将方程式解析为Python中的元组列表 [英] Parse equation to list of tuples in Python

问题描述

我想解析方程式并获取元组列表. 例如，当我输入

I want to parse equations and get a list of tuples. For example, when I enter

2x = 4+3y, 

我想得到

[('', '2', 'x', '='), ('','4','',''), ('+','3','y','')]

到目前为止，这是我的正则表达式:

This is my regex so far:

([+-]*)([0-9]+)([a-z]*)([<=>]*)

对于上面的查询，它工作正常，但不能捕获诸如

It works fine for the above query but it does not capture equations like

2 = x +3y，(其中x没有任何系数)

2 = x +3y, (where x does not have any coefficient)

我该如何捕捉?

推荐答案

如果将系数的量词从+ (一个或多个)更改为* (零或更多)，那么您应该得到想要的结果.由于所有的量词现在都为*，因此您还将得到一个空字符串匹配，但是您可以过滤掉该匹配.

If you change the quantifier on the coefficient from + (one or more) to * (zero or more) then you should get the result you are after. You will also get an empty string match due to all the quantifiers now being * but you can filter out that match.

>>> import re
>>> e1 = "2x=4+3y"
>>> e2 = "2=x+3y"
>>> re.findall("([+-]*)([0-9]*)([a-z]*)([<=>]*)", e1)
[('', '2', 'x', '='), ('', '4', '', ''), ('+', '3', 'y', ''), ('', '', '', '')]
>>> re.findall("([+-]*)([0-9]*)([a-z]*)([<=>]*)", e2)
[('', '2', '', '='), ('', '', 'x', ''), ('+', '3', 'y', ''), ('', '', '', '')]

注意:虽然这可以解决您的直接问题，但这不是解析infix方程的好方法.

Note: whilst this solves your direct question this is not a good approach to parsing infix equations.

这篇关于将方程式解析为Python中的元组列表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！