python runtime_error ai_generated true

StopIteration: raised by side_effect list exhausted

ID: python/unittest-mock-side-effect

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80%Fix Rate
85%Confidence
0Evidence
2024-06-11First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.8 active — — —
3.12 active — — —

Root Cause

A mock's side_effect was set to a finite list, and the code under test called the mock more times than the list length, raising StopIteration.

generic

中文

mock 的 side_effect 被设置为有限列表，而被测代码调用 mock 的次数超过列表长度，引发 StopIteration。

Workarounds

  1. 90% success 
    Use a callable for side_effect that handles any number of calls:

m.side_effect = lambda x: x * 2
  2. 88% success 
    Extend the list to match the expected call count and assert:

m.side_effect = [1, 2, 3]
run()
assert m.call_count == 3

Dead Ends

Common approaches that don't work:

  1. 85% fail

    This hides the real issue: the test exercises more calls than expected, or the list is too short.

  2. 80% fail

    Adding one None only delays the problem; a subsequent call raises StopIteration again.