#!/usr/bin/env python
"""Substitution example
 
Demonstrates substitution.
"""
 
import sympy
 
def main():
    x = sympy.Symbol('x')
    y = sympy.Symbol('y')
 
    e = 1/sympy.cos(x)
    print e
    print e.subs(sympy.cos(x), y)
    print e.subs(sympy.cos(x), y).subs(y, x**2)
 
    e = 1/sympy.log(x)
    e = e.subs(x, sympy.Real("2.71828"))
    print e
    print e.evalf()
 
if __name__ == "__main__":
    main()