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Add metadata to exported functions #3682

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26 changes: 26 additions & 0 deletions docs/src/usage/export.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -109,6 +109,32 @@ keyword arguments when calling the imported function.
out, = imported_fun(x, z=y)


Saving Metadata
---------------

You can save additional metadata, such as a model configuration, alongside an
exported function. The metadata is a dictionary of string keys and string
values:

.. code-block:: python

def fun(x, y):
return x + y

metadata = {"description": "adds two arrays", "version": "1.0"}
mx.export_function("add.mlxfn", fun, x, y, metadata=metadata)

Read the metadata back when importing the function by passing
``return_metadata=True``:

.. code-block:: python

imported_fun, metadata = mx.import_function("add.mlxfn", return_metadata=True)

# Prints: {'description': 'adds two arrays', 'version': '1.0'}
print(metadata)


Exporting Modules
-----------------

Expand Down
53 changes: 36 additions & 17 deletions mlx/export.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -520,10 +520,15 @@ struct PrimitiveFactory {
};
};

void write_header(Writer& os, int count, bool shapeless) {
void write_header(
Writer& os,
int count,
bool shapeless,
const std::unordered_map<std::string, std::string>& metadata) {
serialize(os, std::string(version()));
serialize(os, count);
serialize(os, shapeless);
serialize(os, metadata);
}

// A struct to hold and retrieve the graphs that are exported / imported
Expand Down Expand Up @@ -673,14 +678,16 @@ FunctionTable::Function* FunctionTable::find(
FunctionExporter::FunctionExporter(
const std::string& file,
std::function<std::vector<array>(const Args&, const Kwargs&)> fun,
bool shapeless)
bool shapeless,
std::unordered_map<std::string, std::string> metadata)
: os(file),
fun(std::move(fun)),
ftable(std::make_shared<FunctionTable>(shapeless)) {
ftable(std::make_shared<FunctionTable>(shapeless)),
metadata_(std::move(metadata)) {
if (!os.is_open()) {
throw std::runtime_error("[export_function] Failed to open " + file);
}
write_header(os, count, shapeless);
write_header(os, count, shapeless, metadata_);
}

FunctionExporter::FunctionExporter(
Expand Down Expand Up @@ -812,7 +819,7 @@ void FunctionExporter::export_function(const Args& args, const Kwargs& kwargs) {
// Update the header
auto pos = os.tell();
os.seek(0);
write_header(os, count, ftable->shapeless);
write_header(os, count, ftable->shapeless, metadata_);
os.seek(pos);
serialize(os, kwarg_keys);

Expand Down Expand Up @@ -891,53 +898,61 @@ void FunctionExporter::operator()(const Args& args, const Kwargs& kwargs) {
FunctionExporter exporter(
const std::string& file,
const std::function<std::vector<array>(const Args&)>& fun,
bool shapeless /* = false */) {
bool shapeless /* = false */,
const std::unordered_map<std::string, std::string>& metadata /* = {} */) {
return FunctionExporter{
file,
[fun](const Args& args, const Kwargs&) { return fun(args); },
shapeless};
shapeless,
metadata};
}

FunctionExporter exporter(
const std::string& file,
const std::function<std::vector<array>(const Kwargs&)>& fun,
bool shapeless /* = false */) {
bool shapeless /* = false */,
const std::unordered_map<std::string, std::string>& metadata /* = {} */) {
return exporter(
file,
[fun](const Args&, const Kwargs kwargs) { return fun(kwargs); },
shapeless);
shapeless,
metadata);
}

FunctionExporter exporter(
const std::string& file,
const std::function<std::vector<array>(const Args&, const Kwargs&)>& fun,
bool shapeless /* = false */) {
return FunctionExporter{file, fun, shapeless};
bool shapeless /* = false */,
const std::unordered_map<std::string, std::string>& metadata /* = {} */) {
return FunctionExporter{file, fun, shapeless, metadata};
}

void export_function(
const std::string& file,
const std::function<std::vector<array>(const Args&)>& fun,
const Args& args,
bool shapeless /* = false */) {
exporter(file, fun, shapeless)(args);
bool shapeless /* = false */,
const std::unordered_map<std::string, std::string>& metadata /* = {} */) {
exporter(file, fun, shapeless, metadata)(args);
}

void export_function(
const std::string& file,
const std::function<std::vector<array>(const Kwargs&)>& fun,
const Kwargs& kwargs,
bool shapeless /* = false */) {
exporter(file, fun, shapeless)(kwargs);
bool shapeless /* = false */,
const std::unordered_map<std::string, std::string>& metadata /* = {} */) {
exporter(file, fun, shapeless, metadata)(kwargs);
}

void export_function(
const std::string& file,
const std::function<std::vector<array>(const Args&, const Kwargs&)>& fun,
const Args& args,
const Kwargs& kwargs,
bool shapeless /* = false */) {
exporter(file, fun, shapeless)(args, kwargs);
bool shapeless /* = false */,
const std::unordered_map<std::string, std::string>& metadata /* = {} */) {
exporter(file, fun, shapeless, metadata)(args, kwargs);
}

FunctionExporter exporter(
Expand Down Expand Up @@ -1047,6 +1062,10 @@ ImportedFunction::ImportedFunction(const std::string& file)
auto mlx_version = deserialize<std::string>(is);
auto function_count = deserialize<int>(is);
ftable->shapeless = deserialize<bool>(is);
auto metadata_pairs =
deserialize<std::vector<std::pair<std::string, std::string>>>(is);

@zcbenz zcbenz Jun 16, 2026

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What would happen when importing functions exported from previous versions without metadata support? (There is no need to be compatible but I'm curious about the behavior)

metadata_ = std::unordered_map<std::string, std::string>(
metadata_pairs.begin(), metadata_pairs.end());
std::unordered_map<std::uintptr_t, array> constants;

auto import_one = [&]() {
Expand Down
18 changes: 12 additions & 6 deletions mlx/export.h
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Original file line number Diff line number Diff line change
Expand Up @@ -50,17 +50,20 @@ struct FunctionExporter;
MLX_API FunctionExporter exporter(
const std::string& file,
const std::function<std::vector<array>(const Args&)>& fun,
bool shapeless = false);
bool shapeless = false,
const std::unordered_map<std::string, std::string>& metadata = {});

MLX_API FunctionExporter exporter(
const std::string& file,
const std::function<std::vector<array>(const Kwargs&)>& fun,
bool shapeless = false);
bool shapeless = false,
const std::unordered_map<std::string, std::string>& metadata = {});

MLX_API FunctionExporter exporter(
const std::string& path,
const std::function<std::vector<array>(const Args&, const Kwargs&)>& fun,
bool shapeless = false);
bool shapeless = false,
const std::unordered_map<std::string, std::string>& metadata = {});

/**
* Export a function to a file.
Expand All @@ -69,20 +72,23 @@ MLX_API void export_function(
const std::string& file,
const std::function<std::vector<array>(const Args&)>& fun,
const Args& args,
bool shapeless = false);
bool shapeless = false,
const std::unordered_map<std::string, std::string>& metadata = {});

MLX_API void export_function(
const std::string& file,
const std::function<std::vector<array>(const Kwargs&)>& fun,
const Kwargs& kwargs,
bool shapeless = false);
bool shapeless = false,
const std::unordered_map<std::string, std::string>& metadata = {});

MLX_API void export_function(
const std::string& file,
const std::function<std::vector<array>(const Args&, const Kwargs&)>& fun,
const Args& args,
const Kwargs& kwargs,
bool shapeless = false);
bool shapeless = false,
const std::unordered_map<std::string, std::string>& metadata = {});

struct ImportedFunction;

Expand Down
19 changes: 15 additions & 4 deletions mlx/export_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -27,17 +27,20 @@ struct MLX_API FunctionExporter {
friend MLX_API FunctionExporter exporter(
const std::string&,
const std::function<std::vector<array>(const Args&)>&,
bool shapeless);
bool shapeless,
const std::unordered_map<std::string, std::string>& metadata);

friend MLX_API FunctionExporter exporter(
const std::string&,
const std::function<std::vector<array>(const Kwargs&)>&,
bool shapeless);
bool shapeless,
const std::unordered_map<std::string, std::string>& metadata);

friend MLX_API FunctionExporter exporter(
const std::string&,
const std::function<std::vector<array>(const Args&, const Kwargs&)>&,
bool shapeless);
bool shapeless,
const std::unordered_map<std::string, std::string>& metadata);

friend MLX_API FunctionExporter exporter(
const ExportCallback&,
Expand All @@ -57,7 +60,8 @@ struct MLX_API FunctionExporter {
FunctionExporter(
const std::string& file,
std::function<std::vector<array>(const Args&, const Kwargs&)> fun,
bool shapeless);
bool shapeless,
std::unordered_map<std::string, std::string> metadata);

FunctionExporter(
const ExportCallback& callback,
Expand All @@ -77,6 +81,7 @@ struct MLX_API FunctionExporter {
int count{0};
bool closed{false};
std::shared_ptr<FunctionTable> ftable;
std::unordered_map<std::string, std::string> metadata_;
};

struct MLX_API ImportedFunction {
Expand All @@ -88,12 +93,18 @@ struct MLX_API ImportedFunction {
std::vector<array> operator()(const Kwargs& kwargs) const;
std::vector<array> operator()(const Args& args, const Kwargs& kwargs) const;

// The metadata stored alongside the function when it was exported.
const std::unordered_map<std::string, std::string>& metadata() const {
return metadata_;
}

private:
ImportedFunction(const std::string& file);
friend MLX_API ImportedFunction import_function(const std::string&);
ImportedFunction();

std::shared_ptr<FunctionTable> ftable;
std::unordered_map<std::string, std::string> metadata_;
};

} // namespace mlx::core
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