donnemartin/interactive-coding-challenges · error · KeyError
word does not exist
Error message
word does not exist
What it means
Raised by Trie.remove when the word is not stored as a terminated word in the trie. find returns a node only if the full path exists AND the final node has terminates=True; otherwise remove raises KeyError. Prefixes of stored words also trigger this (e.g. removing 'ab' when only 'abc' is stored).
Solutions
- Check with trie.find(word) first and only remove if it returns a node
- Track deletion state upstream to avoid double-remove
- Catch KeyError and treat 'already absent' as success (idempotent delete)
Example fix
# before
trie.remove(word) # KeyError if absent
# after
if trie.find(word) is not None:
trie.remove(word) Defensive patterns
Strategy: try-catch
Validate before calling
if trie.find(word) is not None:
trie.remove(word) Type guard
def word_in_trie(trie, word) -> bool:
return word is not None and trie.find(word) is not None Try / catch
try:
trie.remove(word)
except KeyError:
pass # word already absent Prevention
- Check with find() before remove
- Make delete handlers idempotent by catching KeyError
When it happens
Trigger: Calling remove on a never-inserted word; removing a word twice; removing a proper prefix of a stored word.
Common situations: Duplicate delete requests in request handling; deleting from stale word lists; assuming prefixes count as words.
Related errors
AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28).
Data as JSON: /api/errors/a66272f1c566a40b.
Report an issue: GitHub.
Appendix: source
Thrown at graphs_trees/trie/trie.py:47
def insert(self, word):
if word is None:
raise TypeError('word cannot be None')
node = self.root
parent = None
for char in word:
if char in node.children:
node = node.children[char]
else:
node.children[char] = Node(char, parent=node)
node = node.children[char]
node.terminates = True
def remove(self, word):
if word is None:
raise TypeError('word cannot be None')
node = self.find(word)
if node is None:
raise KeyError('word does not exist')
node.terminates = False
parent = node.parent
while parent is not None:
# As we are propagating the delete up the
# parents, if this node has children, stop
# here to prevent orphaning its children.
# Or
# if this node is a terminating node that is
# not the terminating node of the input word,
# stop to prevent removing the associated word.
if node.children or node.terminates:
return
del parent.children[node.key]
node = parent
parent = parent.parent
def list_words(self):
result = []View on GitHub (pinned to 358f2cc604)