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

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

def dfs(graph, source):
    # Push current location to the stack.
    stack = [source]

    # While there are still nodes to be visited...
    while len(stack) > 0:
        # Pop the top node off the stack.
        current = stack.pop()
        print(current)

        # Append every neighboring node to the stack.
        for neighbor in graph[current]:
             stack.append(neighbor)