[HELP] Issue resolving KeyError during dictionary iteration over dynamically generated keys

I am iterating through a dict where some keys are removed by a concurrent process or conditional logic, causing KeyErrors mid-loop. The fix I want to confirm: use .items() and .get(key) instead of bracket access, or copy the keyset first with list(d.keys()) to freeze the iteration state?

The issue you're encountering is fundamentally tied to how Python handles key-value pair dereferencing within a for-loop when those same references are being mutated in the underlying container, which introduces several interesting edge cases worth unpacking systematically. Let me walk through this from first principles so we can identify exactly where your specific implementation deviates from expected behavior and why that's causing the KeyError instead of producing the predictable iterator instability one might anticipate from languages with more permissive collection semantics.

First, it is important to clarify what Python actually does when you begin iterating over a dictionary: the for-loop syntax for key in my_dict: implicitly calls the dict's iter method, which produces an iterator that yields keys based on the internal hash table layout at the moment of iteration start. This isn't a snapshot — it's a live view into the container's structure, and this is precisely where things get complicated when you combine iteration with modification operations within the loop body itself.

Let me trace what happens in your specific scenario. You mentioned dynamically generating keys during iteration, which I interpret as inserting new key-value pairs while looping over existing ones. When you execute my_dict[new_key] = value inside a for-loop over my_dict, the hash table may need to rehash if the insertion exceeds the current load factor threshold (typically 2/3 of capacity). A rehash operation completely rebuilds the internal structure, and because your iterator is walking this same structure as it yields, any pointer invalidation or structural reorganization during an active iteration can lead to undefined behavior at the CPython level. The KeyError specifically signals that by the time the iterator advances to a key's hash entry, that entry has been relocated or removed, so even though your loop was nominally iterating over what you thought were stable keys, the underlying container structure shifted beneath it.

There are several related failure modes worth noting here because they share the same

use .get() with default instead of bracket notation

for k, v in

This is literally one of the most common beginner mistakes in Python and it's genuinely exhausting to keep explaining it. You're mutating a dictionary while iterating over its keys, which causes the iterator to lose track when you delete an entry mid-loop. That's not an issue with your