Representing graphs (data structure) in Python

Question

How can one neatly represent a graph in Python? (Starting from scratch i.e. no libraries!)
What data structure (e.g. dicts/tuples/dict(tuples)) will be fast but also mem

Answer 1

There are two excellent graph libraries NetworkX and igraph. You can find both library source codes on GitHub. You can always see how the functions are written. But I prefer NetworkX because its easy to understand.
See their codes to know how they make the functions. You will get multiple ideas and then can choose how you want to make a graph using data structures.