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Reject negative token counts when calculating costs #239

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Reject negative token counts when calculating costs #239

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d11a1af
Reject negative token counts when calculating costs
seanmcrae Oct 23, 2026
1df7ebe
Add negative-token cost regression test
seanmcrae Oct 23, 2026
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5 changes: 5 additions & 0 deletions tests/test_costs.py
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Original file line number Diff line number Diff line change
Expand Up @@ -271,3 +271,8 @@ def test_calculate_cached_tokens_cost():
# Assert that the costs match
assert actual_cost == expected_cost
assert actual_cost > 0, "Cache token cost should be greater than zero"


def test_calculate_cost_by_tokens_rejects_negative_token_counts():
with pytest.raises(ValueError, match="num_tokens must be non-negative"):
calculate_cost_by_tokens(-1, "gpt-4o", "input")
3 changes: 3 additions & 0 deletions tokencost/costs.py
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Expand Up @@ -317,6 +317,9 @@ def calculate_cost_by_tokens(num_tokens: int, model: str, token_type: TokenType)
Returns:
Decimal: The calculated cost in USD.
"""
if num_tokens < 0:
raise ValueError("num_tokens must be non-negative")

model = _normalize_model_for_pricing(model)
if model not in TOKEN_COSTS:
raise KeyError(
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