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fix(core): Filter empty content blocks from formatted prompts #32519

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fix(core): Filter empty content blocks from formatted prompts #32519

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daf25ab
Add test
jacoblee93 Aug 12, 2025
3f60014
Fix
jacoblee93 Aug 12, 2025
0c81d1a
rerun
jacoblee93 Aug 12, 2025
06d8c83
Format
jacoblee93 Aug 12, 2025
bebc6f5
Fix code
jacoblee93 Aug 12, 2025
24cedf6
Async implementation
jacoblee93 Aug 12, 2025
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6 changes: 4 additions & 2 deletions libs/core/langchain_core/prompts/chat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -602,7 +602,8 @@ def format(self, **kwargs: Any) -> BaseMessage:
formatted: Union[str, ImageURL, dict[str, Any]] = prompt.format(
**inputs
)
content.append({"type": "text", "text": formatted})
if formatted:
content.append({"type": "text", "text": formatted})
elif isinstance(prompt, ImagePromptTemplate):
formatted = prompt.format(**inputs)
content.append({"type": "image_url", "image_url": formatted})
Expand Down Expand Up @@ -634,7 +635,8 @@ async def aformat(self, **kwargs: Any) -> BaseMessage:
formatted: Union[str, ImageURL, dict[str, Any]] = await prompt.aformat(
**inputs
)
content.append({"type": "text", "text": formatted})
if formatted:
content.append({"type": "text", "text": formatted})
elif isinstance(prompt, ImagePromptTemplate):
formatted = await prompt.aformat(**inputs)
content.append({"type": "image_url", "image_url": formatted})
Expand Down
347 changes: 347 additions & 0 deletions libs/core/tests/unit_tests/prompts/test_chat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1232,3 +1232,350 @@ def test_dict_message_prompt_template_errors_on_jinja2() -> None:
_ = ChatPromptTemplate.from_messages(
[("human", [prompt])], template_format="jinja2"
)


def test_rendering_prompt_with_conditionals_no_empty_text_blocks() -> None:
manifest = {
"lc": 1,
"type": "constructor",
"id": ["langchain_core", "prompts", "chat", "ChatPromptTemplate"],
"kwargs": {
"messages": [
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"chat",
"SystemMessagePromptTemplate",
],
"kwargs": {
"prompt": {
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "Always echo back whatever I send you.",
},
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"chat",
"HumanMessagePromptTemplate",
],
"kwargs": {
"prompt": [
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "Here is the teacher's prompt:",
"additional_content_fields": {
"text": "Here is the teacher's prompt:",
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["promptDescription"],
"template_format": "mustache",
"template": '"{{promptDescription}}"\n',
"additional_content_fields": {
"text": '"{{promptDescription}}"\n',
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "Here is the expected answer or success criteria given by the teacher:", # noqa: E501
"additional_content_fields": {
"text": "Here is the expected answer or success criteria given by the teacher:", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["expectedResponse"],
"template_format": "mustache",
"template": '"{{expectedResponse}}"\n',
"additional_content_fields": {
"text": '"{{expectedResponse}}"\n',
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "Note: This may be just one example many possible correct ways for the student to respond.\n", # noqa: E501
"additional_content_fields": {
"text": "Note: This may be just one example many possible correct ways for the student to respond.\n", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "For your evaluation of the student's response:\n", # noqa: E501
"additional_content_fields": {
"text": "For your evaluation of the student's response:\n", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "Here is a transcript of the student's explanation:", # noqa: E501
"additional_content_fields": {
"text": "Here is a transcript of the student's explanation:", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["responseTranscript"],
"template_format": "mustache",
"template": '"{{responseTranscript}}"\n',
"additional_content_fields": {
"text": '"{{responseTranscript}}"\n',
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["readingFluencyAnalysis"],
"template_format": "mustache",
"template": "{{#readingFluencyAnalysis}} For this task, the student's reading pronunciation and fluency were important. Here is analysis of the student's oral response: \"{{readingFluencyAnalysis}}\" {{/readingFluencyAnalysis}}", # noqa: E501
"additional_content_fields": {
"text": "{{#readingFluencyAnalysis}} For this task, the student's reading pronunciation and fluency were important. Here is analysis of the student's oral response: \"{{readingFluencyAnalysis}}\" {{/readingFluencyAnalysis}}", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["readingFluencyAnalysis"],
"template_format": "mustache",
"template": "{{#readingFluencyAnalysis}}Root analysis of the student's response (step 3) in this oral analysis rather than inconsistencies in the transcript.{{/readingFluencyAnalysis}}", # noqa: E501
"additional_content_fields": {
"text": "{{#readingFluencyAnalysis}}Root analysis of the student's response (step 3) in this oral analysis rather than inconsistencies in the transcript.{{/readingFluencyAnalysis}}", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["readingFluencyAnalysis"],
"template_format": "mustache",
"template": "{{#readingFluencyAnalysis}}Remember this is a student, so we care about general fluency - not voice acting. {{/readingFluencyAnalysis}}\n", # noqa: E501
"additional_content_fields": {
"text": "{{#readingFluencyAnalysis}}Remember this is a student, so we care about general fluency - not voice acting. {{/readingFluencyAnalysis}}\n", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": ["multipleChoiceAnalysis"],
"template_format": "mustache",
"template": "{{#multipleChoiceAnalysis}}Here is an analysis of the student's multiple choice response: {{multipleChoiceAnalysis}}{{/multipleChoiceAnalysis}}\n", # noqa: E501
"additional_content_fields": {
"text": "{{#multipleChoiceAnalysis}}Here is an analysis of the student's multiple choice response: {{multipleChoiceAnalysis}}{{/multipleChoiceAnalysis}}\n", # noqa: E501
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"prompt",
"PromptTemplate",
],
"kwargs": {
"input_variables": [],
"template_format": "mustache",
"template": "Here is the student's whiteboard:\n",
"additional_content_fields": {
"text": "Here is the student's whiteboard:\n",
},
},
},
{
"lc": 1,
"type": "constructor",
"id": [
"langchain_core",
"prompts",
"image",
"ImagePromptTemplate",
],
"kwargs": {
"template": {
"url": "{{whiteboard}}",
},
"input_variables": ["whiteboard"],
"template_format": "mustache",
"additional_content_fields": {
"image_url": {
"url": "{{whiteboard}}",
},
},
},
},
],
"additional_options": {},
},
},
],
"input_variables": [
"promptDescription",
"expectedResponse",
"responseTranscript",
"readingFluencyAnalysis",
"readingFluencyAnalysis",
"readingFluencyAnalysis",
"multipleChoiceAnalysis",
"whiteboard",
],
"template_format": "mustache",
"metadata": {
"lc_hub_owner": "jacob",
"lc_hub_repo": "mustache-conditionals",
"lc_hub_commit_hash": "836ad82d512409ea6024fb760b76a27ba58fc68b1179656c0ba2789778686d46", # noqa: E501
},
},
}

# Load the ChatPromptTemplate from the manifest
template = load(manifest)

# Format with conditional data - rules is empty, so mustache conditionals
# should not render
result = template.invoke(
{
"promptDescription": "What is the capital of the USA?",
"expectedResponse": "Washington, D.C.",
"responseTranscript": "Washington, D.C.",
"readingFluencyAnalysis": None,
"multipleChoiceAnalysis": "testing2",
"whiteboard": "https://foo.com/bar.png",
}
)
content = result.messages[1].content
assert isinstance(content, list)
assert not [
block for block in content if block["type"] == "text" and block["text"] == ""
]
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