How to find an element that satisfies a condition in the following tree?

Question

Using Python and Selenium how do I find an element that satisfies a condition in the following tree?

(S, A ~ H is Class)

S
├── A
├── B
├── C
│   └── D
├── E
│   └── F
├── G
└── H

When D is present, we want to find the element of F.

Answer 1

If s is the webelement root and we want to check if a class exists within that element we do the following.

elem=s.find_element_by_xpath("//[class='c']/[class='d']")
if elem:
   s.find_element_by_xpath("//[class='e']/[class='f']")