python-3.x - Sympy:如何解析 '2x' 等表达式？

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)

我试图制作一个使用 sympy 来解决代数的不和谐机器人，但我一直遇到上述实现的错误。有人可以帮忙吗？

但是对于输入 10 = 2x parse_expr给出一个语法错误。我如何使用 parse_expr或一些类似的功能来接受这种表达？

错误:

  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允许通过其 transformations= 灵活输入范围。
implicit_multiplication_application允许省略 *什么时候可以假设乘法。很多时候，人们也想要^用于幂，而 Python 标准使用 **电源和储备^为独占或。转型convert_xor负责这种转换。

下面是一个例子:

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)

结果: 3*x*y*z + cos(theta) + 10*tan(x**2)
documentation描述了许多其他可能的变换。应该小心，因为结果并不总是所希望的，尤其是在组合转换时。