Python方程式解析器 [英] Python equation parser

问题描述

我正在编写一个程序，该程序需要用户输入x的多项式函数.我正在使用Tkinter和python 2.5.

I'm writing a program which needs a user input for an polynomial function of x. I'm using Tkinter and python 2.5.

我有一个解析器方法，到目前为止，它采用输入的方程式并将其拆分为项，而不会删除符号.

I have a parser method which so far takes the inputted equation and splits it into terms without dropping the signs.

我想接受每个术语并解析它以获得(系数，度)的元组.例如，-2x ^ 3返回(-2,3).然后，我可以将它们添加到数组中，并在程序中进行相应的操作.

I want to take each term and parse it to get a tuple of the (coefficient, degree). For example, -2x^3 returns (-2,3). I can then add these to an array and manipulate them accordingly in the program.

有没有一种方法或标准模块可以做到这一点?

Is there a way or standard module that can do this?

这是解析方法的开始.

def parse(a):
    termnum=[]
    terms=[]
    hi=[]
    num1=0
    num=0
    f=list(a)

    count=0
    negative=False
    coef=0.0
    deg=0.0
    codeg=[]
    for item in f:
        if (item=='-' or item=='+') and count!=0:
            termnum.append(count)
        count+=1
    for item in termnum:
        num1=num
        num=item
        current=''
        while num1<num:
            current=current+f[num1]
            num1+=1
        terms.append(current)
    num1=num
    num=len(f)
    current=''
    while num1<num:
        current=current+f[num1]
        num1+=1
    terms.append(current)
    print terms
parse('-x^2+3x+2x^3-x')

谢谢！ 附言:我不想使用外部软件包.

Thanks! P.S I don't want to use external packages.

推荐答案

您可以使用正则表达式

import re

test = '-x^2+3x+2x^3-x'

for m in re.finditer( r'(-{0,1}\d*)x\^{0,1}(-{0,1}\d*)', test ):
    coef, expn = list( map( lambda x: x if x != '' and x != '-' else x + '1' ,
                            m.groups( ) ))
    print ( 'coef:{}, exp:{}'.format( coef, expn ))

输出:

coef:-1, exp:2
coef:3, exp:1
coef:2, exp:3
coef:-1, exp:1

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