python - Identifying variables in equation -

i'm trying create calculator receive input formula , data respective variables.

i trying made user friendly possible, in mind user insert formula , code identify variables in formula.

after program ask values correspond each variable.

and question is: "how can parse string in search of variables?" have able identify things "pi" , trigonometric functions, since variable angle.

is there simple way this?

edit: code have far, first aproach on user execute code. trying evade using eval , exec

from scipy import stats import matplotlib.pyplot plt import numpy np math import* import math recept = "."  print("bem vindo calculadora de incertezas com base no metodo monte carlo") formula = input("insira formula desejada:") while (recept != ""):     recept = input("defina variaveis de acordo com o exemplo:\n ex: p = (media,     desviopadrão)")     print (recept)      #aproach one: execute code inserted user: user define variables.     if(recept != ""):         exec(recept)  print (exec(formula)) 

this should started:

>>> import re  >>> formula = "p = v*i*cos(2*pi*f)" >>> variables = re.findall('[a-za-z]+' , formula) ['p', 'v', 'i', 'cos', 'pi', 'f'] >>> special = ['cos', 'pi'] >>> variables = [v v in variables if v not in special]   ['p', 'v', 'i', 'f'] 

from here can improve regular expression account more complex variable names (ex: v1)