How do I parse strings in python for substrings,then graph the occurrence of each substring in matplotlib?

This is a cheminformatics question,I'm trying to parse 300 strings each representing a specific chemical in smiles format, so let's say I have strings "CCC=C", "CCCCC=O' , "CCCCCC" and I want to parse for the occurrence of "CCC" and plot the result in a graph,how would I do it?