title: How do I evaluate a single variable function with exponential with SymPy?
body: <p>I'm trying to use SymPy to calculate some expressions, but sometimes, using the <code>.subs()</code> function alone, or followed by <code>.evalf()</code>, does not give any float or integer values.</p>
  
  <pre><code>##--IMPORT
  from mpmath import *
  from sympy import *
  from sympy.parsing.sympy_parser import parse_expr
  
  x = symbols("x")
  
  _fOfX = "e**x + x + 1"
  
  if __name__== "__main__":
      #Function to sympy expression
      _sympyFunction = sympify(_fOfX)
      #Calcolo la derivata prima
      _dPrima = diff(_sympyFunction,x,1)
      _dPrima = _dPrima.subs(x,5)
  
      print(_dPrima.evalf())
  </code></pre>
  
  <p>And for those who want to know, yes I need to parse a string to get the function.</p>