python type_error ai_generated true

TypeError: 'NoneType' object is not subscriptable

ID: python/typeerror-nonetype-not-subscriptable

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85%Fix Rate
88%Confidence
290Evidence
2023-01-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
311 active — — —

Root Cause

Occurs when indexing or iterating over a None value. Usually a missing return or failed API call.

generic

Workarounds

  1. 90% success Trace the variable back to its assignment and fix the source of None 
    Add breakpoint or print before assignment

    Sources: https://docs.python.org/3/library/functions.html#breakpoint

  2. 85% success Use Optional type hints and handle None explicitly in the function that produces the value 
    Use Optional type hints and handle None explicitly in the function that produces the value

    Sources: https://docs.python.org/3/library/typing.html#typing.Optional

Dead Ends

Common approaches that don't work:

  1. Add try/except around the indexing 72% fail

    Masks the root cause without fixing the None source

  2. Check if variable is None right before use 65% fail

    The None originates earlier in the call chain

Error Chain

Leads to:
Preceded by: