所有sympy对象都从sympy.Basic继承.要以数值方式计算sympy表达式，只需使用.n()

All sympy objects inherit from sympy.Basic. To evaluate an sympy expression numerically, just use .n()

In [1]: import sympy

In [2]: x = sympy.sqrt(2)

In [3]: x
Out[3]: sqrt(2)

In [4]: x.n()
Out[4]: 1.41421356237310

In [5]: if (isinstance(x, sympy.Basic)):
   ...:     print(x.n())
   ...:     
1.41421356237310