Parsing a 4th degree equation in python-CodePudding

kinda noob here. So, please forgive me.

I'd like to pars a 4th degree string equations to its components and I wonder what kind of Regex will I need. Let's say the equation are :

"x^4 5x^3 - 2x - 18"

I'd like to turn this into [x^4, 5x^3, -2x, -18]

Thank you

CodePudding user response：

Not sure this needs a regular expression. It's a simple parsing problem.

expr = "x^4   5x^3 - 2x - 18"

token = ''
tokens = []
for c in expr:
    if c == ' ':
        tokens.append(token)
        token = ''
    elif c == '-':
        tokens.append(token)
        token = '-'
    elif c != ' ':
        token  = c
tokens.append(token)
print(tokens)

Output:

['x^4', '5x^3', '-2x', '-18']

CodePudding user response：

Here is one I came up with for your case, if it as simple as that then this would work fine, but if we need to start getting parenthesis involved that is a whole new pickle :D. I had trouble getting the last value for some reason so I just put an | in there.

(?<=\s|\b|[\-\ ])((\d )|(\d*(\w\^*\d*)))(?=\s|\b|[\-\ ])

where ((\d )|(\d*(\w\^*\d*))) is the central piece that actually captures your groups and the lookbehind and lookahead set the edges.

You can play around with it at https://www.regexpal.com/