I am trying to write a program to define user-defined function with return expression as input from user. Suppose a function should return x+y.In python we can do it as---
def f(x,y):
return x+y
But,i want something like
a=input("enter the function:")
def f(x,y):
return a
print f(2,3)
If i enter x+y as input of a,it will give 5.How can it be done in Python(without Sympy or raw_function along with eval())?
This was actually easy.Suppose u want to evaluate the function at x=2
f1=str(input("Enter the test function:"))
def f(x):
return eval(f1)
print f(2)
That's it!
The Pyparsing lib parses mathematical expressions.
You can use it like this for example :
from pyparsing import NumericStringParser
nsp = NumericStringParser()
print(nsp.eval('2+3')) # 5
You have to replace variables by numeric values.
In case your really don't want to use external eval library, an application of RPN could be a solution.
