A concise recursive version of depth-first search (DFS) in Python.

dfs_rec.py

"""
Assume we have a graph modeled as a dictionary like so:
graph = {
  'a': ['b', 'c'],
  'b': ['d'],
  'c': ['e'],
  'd': ['f'],
  'e': [],
  'f': []
}

dfs_rec will traverse this graph using depth-first search.
"""

def dfs_rec(graph, source):
	print(source)
	
	for neighbor in graph[source]:
		dfs_rec(graph, neighbor)