Skip to content

_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230

Closed
Bug
#241
Closed
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
Bug
#241
Assignees
AbhiPrasad

Description

@willfrey
Will Frey (willfrey)
opened on Apr 8, 2026

Summary

braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:

forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising

This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.

Repro

fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'

Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.

Why this is a problem

  1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
  2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
  3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
  4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.

Expected behavior

One of:

  • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
  • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
  • At minimum, document this behavior prominently in the scorer authoring docs.

Workaround

Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.

Environment

  • braintrust (latest on PyPI as of 2026-04-08)
  • Python 3.14

Metadata

Metadata

Assignees

Labels

No labels
No labels

Type

Bug

Projects

No projects

    Milestone

    No milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions

    , 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
     blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
    Skip to content
    _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
    Closed
    Bug
    #241
    Closed
    _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
    Bug
    #241
    Assignees
    AbhiPrasad
    Description
    @willfrey
    Will Frey (willfrey)
    opened on Apr 8, 2026
    Summary
    braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
    forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
    This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
    Repro
    fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
    Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
    Why this is a problem
    1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
    2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
    3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
    4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
    Expected behavior
    One of:
    • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
    • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
    • At minimum, document this behavior prominently in the scorer authoring docs.
    Workaround
    Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
    Environment
    • braintrust (latest on PyPI as of 2026-04-08)
    • Python 3.14
    Metadata
    Metadata
    Assignees
    Labels
    No labels
    No labels
    Type
    Bug
    Projects
    No projects
      Milestone
      No milestone
      Relationships
      None yet
      Development
      No branches or pull requests
      Issue actions
      
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
      Skip to content
      _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
      Closed
      Bug
      #241
      Closed
      _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
      Bug
      #241
      Assignees
      AbhiPrasad
      Description
      @willfrey
      Will Frey (willfrey)
      opened on Apr 8, 2026
      Summary
      braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
      forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
      This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
      Repro
      fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
      Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
      Why this is a problem
      1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
      2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
      3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
      4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
      Expected behavior
      One of:
      • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
      • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
      • At minimum, document this behavior prominently in the scorer authoring docs.
      Workaround
      Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
      Environment
      • braintrust (latest on PyPI as of 2026-04-08)
      • Python 3.14
      Metadata
      Metadata
      Assignees
      Labels
      No labels
      No labels
      Type
      Bug
      Projects
      No projects
        Milestone
        No milestone
        Relationships
        None yet
        Development
        No branches or pull requests
        Issue actions
        
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
        Skip to content
        _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
        Closed
        Bug
        #241
        Closed
        _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
        Bug
        #241
        Assignees
        AbhiPrasad
        Description
        @willfrey
        Will Frey (willfrey)
        opened on Apr 8, 2026
        Summary
        braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
        forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
        This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
        Repro
        fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
        Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
        Why this is a problem
        1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
        2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
        3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
        4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
        Expected behavior
        One of:
        • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
        • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
        • At minimum, document this behavior prominently in the scorer authoring docs.
        Workaround
        Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
        Environment
        • braintrust (latest on PyPI as of 2026-04-08)
        • Python 3.14
        Metadata
        Metadata
        Assignees
        Labels
        No labels
        No labels
        Type
        Bug
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
          Skip to content
          _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
          Closed
          Bug
          #241
          Closed
          _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
          Bug
          #241
          Assignees
          AbhiPrasad
          Description
          @willfrey
          Will Frey (willfrey)
          opened on Apr 8, 2026
          Summary
          braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
          forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
          This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
          Repro
          fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
          Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
          Why this is a problem
          1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
          2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
          3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
          4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
          Expected behavior
          One of:
          • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
          • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
          • At minimum, document this behavior prominently in the scorer authoring docs.
          Workaround
          Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
          Environment
          • braintrust (latest on PyPI as of 2026-04-08)
          • Python 3.14
          Metadata
          Metadata
          Assignees
          Labels
          No labels
          No labels
          Type
          Bug
          Projects
          No projects
            Milestone
            No milestone
            Relationships
            None yet
            Development
            No branches or pull requests
            Issue actions
            
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
            Skip to content
            _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
            Closed
            Bug
            #241
            Closed
            _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
            Bug
            #241
            Assignees
            AbhiPrasad
            Description
            @willfrey
            Will Frey (willfrey)
            opened on Apr 8, 2026
            Summary
            braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
            forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
            This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
            Repro
            fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
            Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
            Why this is a problem
            1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
            2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
            3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
            4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
            Expected behavior
            One of:
            • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
            • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
            • At minimum, document this behavior prominently in the scorer authoring docs.
            Workaround
            Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
            Environment
            • braintrust (latest on PyPI as of 2026-04-08)
            • Python 3.14
            Metadata
            Metadata
            Assignees
            Labels
            No labels
            No labels
            Type
            Bug
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
              Skip to content
              _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
              Closed
              Bug
              #241
              Closed
              _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
              Bug
              #241
              Assignees
              AbhiPrasad
              Description
              @willfrey
              Will Frey (willfrey)
              opened on Apr 8, 2026
              Summary
              braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
              forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
              This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
              Repro
              fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
              Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
              Why this is a problem
              1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
              2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
              3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
              4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
              Expected behavior
              One of:
              • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
              • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
              • At minimum, document this behavior prominently in the scorer authoring docs.
              Workaround
              Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
              Environment
              • braintrust (latest on PyPI as of 2026-04-08)
              • Python 3.14
              Metadata
              Metadata
              Assignees
              Labels
              No labels
              No labels
              Type
              Bug
              Projects
              No projects
                Milestone
                No milestone
                Relationships
                None yet
                Development
                No branches or pull requests
                Issue actions
                
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();
_call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter · Issue #230 · braintrustdata/braintrust-sdk-python · GitHub
                Skip to content
                _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter #230
                Closed
                Bug
                #241
                Closed
                _call_user_fn_args silently reassigns kwargs positionally when a scorer declares an unrelated parameter#230
                Bug
                #241
                Assignees
                AbhiPrasad
                Description
                @willfrey
                Will Frey (willfrey)
                opened on Apr 8, 2026
                Summary
                braintrust.framework._call_user_fn_args (framework.py:488) matches scorer parameters to Braintrust-provided kwargs by name — but when a declared parameter name is not in the provided kwargs, it pops the next available kwarg positionally and assigns it anyway:
                forname, paraminsignature.parameters.items():
ifparam.kindin (VAR_POSITIONAL, VAR_KEYWORD):
continueifnameinkwargs:
final_kwargs[name] =kwargs.pop(name)
else:
next_arg=list(kwargs.keys())[0]
final_kwargs[name] =kwargs.pop(next_arg) # <-- surprising
                This means any scorer that declares a keyword-only parameter whose name Braintrust doesn't inject (e.g. for dependency injection, configuration, a client, a cached resource) will silently receive one of Braintrust's own kwargs — typically metadata or trace — under the wrong name. The declared default is discarded.
                Repro
                fromdataclassesimportdataclass@dataclassclassConfig:
threshold: float=0.5DEFAULT_CONFIG=Config()
asyncdefmy_scorer(
input: str,
output,
expected,
*,
config: Config=DEFAULT_CONFIG, # default silently ignored**_,
):
# At runtime, `config` is actually the `metadata` dict that# Braintrust passed, not DEFAULT_CONFIG.returnconfig.threshold# AttributeError: 'dict' object has no attribute 'threshold'
                Braintrust calls scorers with input, expected, metadata, output, trace (framework.py:1571). Because config isn't in that set, _call_user_fn_args pops metadata off the dict and assigns it to config. **_ is populated only with whatever remains after the walk.
                Why this is a problem
                1. Silent type-punning. The scorer parameter has a declared default and a declared type; both are ignored with no warning.
                2. Order-dependent. Which kwarg gets reassigned depends on the insertion order of the kwargs dict — subtle and fragile.
                3. Breaks DI patterns. The natural way to make a scorer testable is to accept an injectable dependency with a default; this behavior makes that unsafe.
                4. No warning or error. The user only notices when the wrong-type value explodes deep in the call stack.
                Expected behavior
                One of:
                • Only bind parameters that are present in Braintrust's provided kwargs by name; leave declared-but-absent parameters to their defaults.
                • If reassignment is intentional for some backward-compat reason, raise or warn when a declared parameter name has no matching kwarg and is filled positionally.
                • At minimum, document this behavior prominently in the scorer authoring docs.
                Workaround
                Drop the extra keyword parameter from the scorer's public signature and reference the dependency from a module-level variable (or closure). Monkeypatch the module-level variable for tests.
                Environment
                • braintrust (latest on PyPI as of 2026-04-08)
                • Python 3.14
                Metadata
                Metadata
                Assignees
                Labels
                No labels
                No labels
                Type
                Bug
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions