Iterative DFS with Explicit Stack

Concepts: pyIterativeDFS, pyExplicitStack, pyRecursionLimit

Python's default recursion limit is 1000 frames. sys.setrecursionlimit() is a band-aid, not a fix. In production, you should never rely on deep recursion. For trees with thousands of nodes (a deep lineage DAG, a very unbalanced parse tree), you need iterative DFS with an explicit stack. The good news: once you understand it, iterative DFS is not that much harder than recursive DFS. You are just managing the call stack yourself instead of letting Python do it. Iterative Pre-Order DFS Iterative In-Order DFS (the Harder One) In-order iterative is trickier because you cannot process a node until you have fully explored its left subtree. The pattern: keep drilling left and pushing nodes onto the stack, then when you cannot go further left, pop and process, then move to the right child and repea