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🐛 Fix TypeError when encoding a decimal with a NaN or Infinity value #12935

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Merged
tiangolo merged 7 commits into from
Dec 2, 2025
Merged

🐛 Fix TypeError when encoding a decimal with a NaN or Infinity value #12935

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c02c16b
[Fix] decimal_encoder function handle 'NaN' and 'Infinity' edge cases
kentwelcome Nov 14, 2024
70037c9
[Fix] Lint issue remove unused type: ignore comment
kentwelcome Nov 25, 2024
32648dc
Merge branch 'master' into fix/decimal_encoder-handles-nan-and-inf-cases
kentwelcome Nov 26, 2024
e291fba
Merge branch 'master' into fix/decimal_encoder-handles-nan-and-inf-cases
kentwelcome Jan 21, 2025
38cffa6
[Fix] Code review suggestions
kentwelcome Sep 12, 2025
73c5b7e
[Fix] lint error - trailing-whitespace
kentwelcome Sep 12, 2025
2900666
[Fix] code review suggestion
kentwelcome Sep 12, 2025
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12 changes: 8 additions & 4 deletions fastapi/encoders.py
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Original file line number Diff line number Diff line change
Expand Up @@ -32,14 +32,14 @@ def isoformat(o: Union[datetime.date, datetime.time]) -> str:
return o.isoformat()


# Taken from Pydantic v1 as is
# Adapted from Pydantic v1
# TODO: pv2 should this return strings instead?
def decimal_encoder(dec_value: Decimal) -> Union[int, float]:
"""
Encodes a Decimal as int of there's no exponent, otherwise float
Encodes a Decimal as int if there's no exponent, otherwise float

This is useful when we use ConstrainedDecimal to represent Numeric(x,0)
where a integer (but not int typed) is used. Encoding this as a float
where an integer (but not int typed) is used. Encoding this as a float
results in failed round-tripping between encode and parse.
Our Id type is a prime example of this.

Expand All @@ -48,8 +48,12 @@ def decimal_encoder(dec_value: Decimal) -> Union[int, float]:

>>> decimal_encoder(Decimal("1"))
1

>>> decimal_encoder(Decimal("NaN"))
nan
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kentwelcome marked this conversation as resolved.
"""
if dec_value.as_tuple().exponent >= 0: # type: ignore[operator]
exponent = dec_value.as_tuple().exponent
if isinstance(exponent, int) and exponent >= 0:
return int(dec_value)
else:
return float(dec_value)
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15 changes: 15 additions & 0 deletions tests/test_jsonable_encoder.py
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Expand Up @@ -3,6 +3,7 @@
from datetime import datetime, timezone
from decimal import Decimal
from enum import Enum
from math import isinf, isnan
from pathlib import PurePath, PurePosixPath, PureWindowsPath
from typing import Optional

Expand Down Expand Up @@ -303,6 +304,20 @@ def test_decimal_encoder_int():
assert jsonable_encoder(data) == {"value": 2}


@needs_pydanticv2
def test_decimal_encoder_nan():
data = {"value": Decimal("NaN")}
assert isnan(jsonable_encoder(data)["value"])


@needs_pydanticv2
def test_decimal_encoder_infinity():
data = {"value": Decimal("Infinity")}
assert isinf(jsonable_encoder(data)["value"])
data = {"value": Decimal("-Infinity")}
assert isinf(jsonable_encoder(data)["value"])


def test_encode_deque_encodes_child_models():
class Model(BaseModel):
test: str
Expand Down