Sympy: How to parse expressions such as '2x'?

Question

            #split the equation into 2 parts using the = sign as the divider, parse, and turn into an equation sympy can understand
            equation = Eq(parse_expr(<input string>.split("=")[0]), parse_expr(<input string>.split("=")[1]))
            answers = solve(equation)
            #check for answers and send them if there are any
            if answers.len == 0:
                response = "There are no solutions!"
            else:
                response = "The answers are "
                for answer in answers:
                    response = response + answer + ", "
                response = response[:-2]
        await self.client.send(response, message.channel)

I was trying to make a discord bot that used sympy to solve algebra but I kept running into errors with the implementation above. Can someone please help?

But for the input 10 = 2x parse_expr gives a syntax error. How can I use parse_expr or some similar function to accept this kind of expressions?

Error:

  File "C:\Users\RealAwesomeness\Documents\Github\amber\amber\plugins/algebra.py", line 19, in respond
    equation = Eq(parse_expr(c[2].split("=")[0]),parse_expr(c[2].split("=")[1]))
  File "C:\Users\RealAwesomeness\AppData\Local\Programs\Python\Python38-32\lib\site-packages\sympy\parsing\sympy_parser.py", line 1008, in parse_expr
    return eval_expr(code, local_dict, global_dict)
  File "C:\Users\RealAwesomeness\AppData\Local\Programs\Python\Python38-32\lib\site-packages\sympy\parsing\sympy_parser.py", line 902, in eval_expr
    expr = eval(
  File "<string>", line 1
    Integer (2 )Symbol ('x' )
                ^
SyntaxError: invalid syntax

Answer 1

parse_expr allows flexible input via its transformations= parameter.

The implicit_multiplication_application allows among others to leave out the * when a multiplication can be presumed. Very often, people also want ^ for powers, while Python standard uses ** for power and reserves ^ for exclusive or. The transformation convert_xor takes care of that conversion.

Here is an example:

from sympy.parsing.sympy_parser import parse_expr, standard_transformations, implicit_multiplication_application, convert_xor

transformations = (standard_transformations + (implicit_multiplication_application,) + (convert_xor,))

expr = parse_expr("10tan x^2 + 3xyz + cos theta",
                  transformations=transformations)

result: 3*x*y*z + cos(theta) + 10*tan(x**2)

The documentation describes many other possible transforms. Care should be taken, because the result is not always what is hoped for, especially when combining transformations.