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The REPL offers functionality for inserting, deleting, and searching within a red-black tree, along with the capability to generate an ASCII or graphical representation of the tree structure.

#!/usr/bin/env python3

import sys

from plot import plot_tree
from rbtree import RedBlackTree

COMMANDS = {
    "insert": lambda rbt, x: rbt.insert(x),
    "delete": lambda rbt, x: rbt.delete(x),
    "search": lambda rbt, x: print(rbt.search(x).get_key()),
    "print": lambda rbt: rbt.print_tree(),
    "plot": lambda rbt: plot_tree(rbt.get_root()),
    "exit": lambda rbt: exit(""),
}


def repl_loop() -> None:
    rbt = RedBlackTree()

    while True:
        try:
            line = input(">> ").rstrip()
        except EOFError:
            exit("")

        tokens = line.split()

        if not tokens:
            continue

        cmd = tokens[0]

        if cmd not in COMMANDS:
            print(f"Error: unknown command: {cmd}.")
            continue

        if cmd in {"print", "exit", "plot"}:
            if len(tokens) != 1:
                print("Error: extra argument.")
                continue
            COMMANDS[cmd](rbt)
            continue
        elif len(tokens) != 2:
            print("Error: expected 2 arguments.")
            continue
        COMMANDS[cmd](rbt, tokens[1])


def main() -> None:
    prompt = (
        "Welcome to RB-Tree REPL.\n"
        "Commands available: insert, delete, search, print, plot, exit.\n"
    )

    print(prompt)
    repl_loop()


if __name__ == "__main__":
    main()

The code has been formatted with black and isort.

Review Request:

Anything. Everything.

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2 Answers 2

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It doesn't make sense to pass a string to exit. That's supposed to be an integer returned to the operating system and accessible by a shell as the return code. If you want to indicate success, use 0 instead.

Don't use lambdas if you don't have to -

  • insert and delete can be non-bound references to RedBlackTree.insert and RedBlackTree.delete respectively
  • search should just be a function
  • print should be a non-bound reference to RedBlackTree.print_tree
  • plot should just be a function

Really, you don't need to do length checking at all. Just splat-pass your *tokens to the method, and if it throws, catch and print a message.

You should probably case-fold your command.

Don't hard-code your Commands available list; form that from a join() on your dictionary keys.

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  • \$\begingroup\$ exit takes strings, but passing it a string is inappropriate here. If you pass it a string, it's treated as an error message. The exit code is 1 (indicating an error) and the string gets printed before exiting. \$\endgroup\$ Apr 10 at 1:16
  • 1
    \$\begingroup\$ (Also exit is only supposed to be used in interactive mode, not in programs. Some Python execution settings don't actually have exit. You're supposed to use sys.exit instead.) \$\endgroup\$ Apr 10 at 1:17
3
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LGTM.

lambdas

Clearly the lambdas work, as-is.

Consider using def instead, in a dedicated module so we can iterate over them. This would open up new possibilities, such as tacking on a number-of-args decorator. Consider adding type annotations.

DRY

COMMANDS = {
    "insert": lambda rbt, x: rbt.insert(x),
    ...

def repl_loop() -> None:
        ...
        if cmd in {"print", "exit", "plot"}:
            if len(tokens) != 1:

This feels a bit redundant and hackish.

Consider putting num_args next to the function definition:

    "insert": (2, lambda rbt, x: rbt.insert(x)),

Consider using try to detect when a "call with wrong number of args" failed, so you can print an informative diagnostic.

Consider using the inspect module to learn how many args a lambda requires.

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2
  • \$\begingroup\$ Re DRY: this should be a namedtuple, probably. \$\endgroup\$ Apr 17 at 21:53
  • 1
    \$\begingroup\$ @SUTerliakov, Agreed, I am usually quite pleased to see namedtuple incorporated into someone’s design. \$\endgroup\$
    – J_H
    Apr 17 at 22:03

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