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