Based off of Mark Nelson's C implementation of Ukkonen's algorithm. Ukkonen's algorithm gives a O(n) O(k) contruction time for a suffix tree, where n is the length of the string and k is the size of the alphabet of that string. Ukkonen's is an online algorithm, processing the input sequentially and producing a valid suffix tree at each character.

string = "I need to be searched!"
tree = SuffixTree(string)
index_of_need = tree.find_substring("need")

This library is mostly an academic exercise. If you need an efficient library I would recommend a python-wrapped c implementation, such as this one.