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fix(tracing): widen Span.set_tag value annotation to match implementation #19814

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fix(tracing): widen Span.set_tag value annotation to match implementation #19814

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fix(tracing): widen Span.set_tag value annotation to match implementa…
ruidc Aug 22, 2026
a79c7c6
docs(tracing): qualify the numeric handling in set_tag docstring
ruidc Aug 24, 2026
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18 changes: 11 additions & 7 deletions ddtrace/_trace/span.py
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Original file line number Diff line number Diff line change
Expand Up @@ -240,13 +240,17 @@ def _set_sampling_decision_maker(
self.context._meta[SAMPLING_DECISION_TRACE_TAG_KEY] = value
return value

def set_tag(self, key: str, value: Optional[str] = None) -> None:
"""Set a tag key/value pair on the span."""
def set_tag(self, key: str, value: Any = None) -> None:
"""Set a tag key/value pair on the span.

Boolean and bytes values are stored as their string representation.
``int`` and ``float`` values are stored as metrics (see ``set_metric``).

@chatgpt-codex-connector chatgpt-codex-connector Bot Aug 22, 2026

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P2 Badge Qualify the numeric-to-metric guarantee

For integers outside the signed 64-bit range or non-finite floats, this new public documentation is incorrect: extract_attribute in src/native/span/span_data.rs stringifies overflowing integers and drops NaN/Infinity rather than storing them as metrics. Callers relying on this documented guarantee will therefore find a string tag or no value at all, so the sentence should state the supported numeric range and finite-value restriction. This docstring is customer-facing because Span is exposed through ddtrace.trace.

AGENTS.md reference: AGENTS.md:L25-L30

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@ruidc ruidc Aug 24, 2026

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Confirmed — thanks, this is a fair catch on a line I added. Fixed in a79c7c6.

I verified it against extract_attribute in src/native/span/span_data.rs (overflowing ints fall through to the str() fallback; NaN/Inf return None) and then measured it through the public set_tag path on 4.13.1:

s.set_tag("small_int", 2**53 + 1)
s.set_tag("i64_max", 2**63 - 1)
s.set_tag("overflow_int", 2**63)
s.set_tag("big_neg", -(2**63) - 1)
s.set_tag("nan", float("nan"))
s.set_tag("inf", float("inf"))
s.set_tag("plain_float", 1.5)
METRICS: {'plain_float': 1.5, 'i64_max': 9223372036854775807, 'small_int': 9007199254740993}
TAGS:    {'overflow_int': '9223372036854775808', 'big_neg': '-9223372036854775809'}

So integers beyond the signed 64-bit range become string tags, and NaN/infinite floats are dropped from both get_metrics() and get_tags() — my unqualified sentence was wrong on both counts.

One addition: there is a third exception the comment doesn't mention. http.status_code has a dedicated always-stringify path in extract_attribute, so an int there is also not stored as a metric:

s.set_tag("http.status_code", 200)
METRICS: {}
TAGS:    {'http.status_code': '200'}

The docstring now states the 64-bit range, the finite-value restriction, and the http.status_code case.

"""
# Explicitly try to convert expected integers to `int`
# DEV: Some integrations parse these values from strings, but don't call `int(value)` themselves
if key == net.TARGET_PORT:
try:
value = int(value) # type: ignore
value = int(value)
except (ValueError, TypeError):
pass

Expand All @@ -261,14 +265,14 @@ def set_tag(self, key: str, value: Optional[str] = None) -> None:
elif key == SERVICE_VERSION_KEY:
# Also set the `version` tag to the same value
# DEV: Note that we do no return, we want to set both
self._set_attribute(VERSION_KEY, value) # type: ignore[arg-type]
self._set_attribute(VERSION_KEY, value)
elif key == _SPAN_MEASURED_KEY:
# Set `_dd.measured` tag as a metric
# DEV: `set_metric` will ensure it is an integer 0 or 1
if value is None:
value = 1 # type: ignore
value = 1

self.set_metric(key, value) # type: ignore[arg-type] # ast-grep-ignore: span-set-metric
self.set_metric(key, value) # ast-grep-ignore: span-set-metric
return

if isinstance(key, bytes):
Expand All @@ -278,7 +282,7 @@ def set_tag(self, key: str, value: Optional[str] = None) -> None:
value = str(value)

try:
self._set_attribute(key, value) # type: ignore[arg-type]
self._set_attribute(key, value)
except Exception:
log.warning("error setting tag %s, ignoring it", key, exc_info=True)

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8 changes: 8 additions & 0 deletions releasenotes/notes/widen-set-tag-value-typing-40a41e0a8804ec18.yaml
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@@ -0,0 +1,8 @@
---
fixes:
- |
tracing: This fix resolves an issue where type checkers rejected valid application code passing
non-string values to ``Span.set_tag`` (for example ``span.set_tag("custom.tag", True)``). The
``value`` parameter was annotated as ``Optional[str]``, but the implementation accepts the
historic domain: booleans and bytes are stringified into tags, and numeric values are stored
as metrics.