Using sympy on strings
Question: I have a file with some equations. I want to solve them using sympy. I can use
open('problems.txt',mode='r') to open the file. But how to proceed with sympy?
I'm getting following error

> sympy.core.sympify.SympifyError: Sympify of expression 'could not parse
> 'x+x+x-x = 18 + 4'' failed, because of exception being raised: SyntaxError:
> invalid syntax (, line 1)

I'm using Python 3.4.2


Answer: [parse_expr](http://docs.sympy.org/dev/modules/parsing.html#sympy.parsing.sympy_parser.parse_expr)
should be able to get you going:

    
    
    import sympy
    
    from sympy.parsing.sympy_parser import (
        parse_expr, standard_transformations,
        implicit_multiplication_application
    )
    
    s = 'x+x+x-x = 18 + 4'
    
    def my_parse(s, transfm=None):
        lhs, rhs = s.split('=')
        if transfm is None:
            transfm = (standard_transformations +
                (implicit_multiplication_application,))
        return sympy.Eq(
            parse_expr(lhs, transformations=transfm),
            parse_expr(rhs, transformations=transfm))
    
    expr = my_parse(s)
    print(expr)
    

output:

    
    
    2*x == 22
    

using sympy version 0.7.6

