Python: Combinations of parent-child hierarchy

Question

For a child-parent relationship table (csv), I am trying to gather possible parent to child relationship combination chains using all data in the table. I am trying against

Answer 1

Have you looked at this fantastic essay? It is essential reading to really understand patterns in python. Your problem can be thought of as a graph problem - finding the relationships is basically finding all paths from a child node to the parent node.

Since there could be an arbitrary amount of nesting (child->parent1->parent2...), you need a recursive solution to find all paths. In your code, you have 2 for loops - which will only result in 3level paths at most as you found out.

The code below was adapted from the link above to fix your issue. The function find_all_paths requires a graph as an input.

Let's create the graph from your file:

graph = {} # Graph is a dictionary to hold our child-parent relationships.
with open('testing.csv','r') as f:
    for row in f:
        child, parent = row.split(',')
        graph.setdefault(parent, []).append(child)

print graph

with your sample, this should print:

{'C': ['A', 'B'], 'B': ['A'], 'D': ['B', 'C']}

The following code is straight from the essay:

def find_all_paths(graph, start, end, path=[]):
    path = path + [start]
    if start == end:
        return [path]

    if not graph.has_key(start):
        return []

    paths = []

    for node in graph[start]:
        if node not in path:
            newpaths = find_all_paths(graph, node, end, path)
            for newpath in newpaths:
                paths.append(newpath)
    return paths

for path in find_all_paths(graph, 'D', 'A'):
    print '|'.join(path)

Output:

D|B|A
D|C|A
D|C|B|A