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//===- PybindUtils.h - Utilities for interop with pybind11 ------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "mlir-c/Support.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/Twine.h"
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
namespace mlir {
namespace python {
// Sets a python error, ready to be thrown to return control back to the
// python runtime.
// Correct usage:
// throw SetPyError(PyExc_ValueError, "Foobar'd");
pybind11::error_already_set SetPyError(PyObject *excClass,
const llvm::Twine &message);
/// CRTP template for special wrapper types that are allowed to be passed in as
/// 'None' function arguments and can be resolved by some global mechanic if
/// so. Such types will raise an error if this global resolution fails, and
/// it is actually illegal for them to ever be unresolved. From a user
/// perspective, they behave like a smart ptr to the underlying type (i.e.
/// 'get' method and operator-> overloaded).
/// Derived types must provide a method, which is called when an environmental
/// resolution is required. It must raise an exception if resolution fails:
/// static ReferrentTy &resolve()
/// They must also provide a parameter description that will be used in
/// error messages about mismatched types:
/// static constexpr const char kTypeDescription[] = "<Description>";
template <typename DerivedTy, typename T>
class Defaulting {
using ReferrentTy = T;
/// Type casters require the type to be default constructible, but using
/// such an instance is illegal.
Defaulting() = default;
Defaulting(ReferrentTy &referrent) : referrent(&referrent) {}
ReferrentTy *get() const { return referrent; }
ReferrentTy *operator->() { return referrent; }
ReferrentTy *referrent = nullptr;
} // namespace python
} // namespace mlir
namespace pybind11 {
namespace detail {
template <typename DefaultingTy>
struct MlirDefaultingCaster {
PYBIND11_TYPE_CASTER(DefaultingTy, _(DefaultingTy::kTypeDescription));
bool load(pybind11::handle src, bool) {
if (src.is_none()) {
// Note that we do want an exception to propagate from here as it will be
// the most informative.
value = DefaultingTy{DefaultingTy::resolve()};
return true;
// Unlike many casters that chain, these casters are expected to always
// succeed, so instead of doing an isinstance check followed by a cast,
// just cast in one step and handle the exception. Returning false (vs
// letting the exception propagate) causes higher level signature parsing
// code to produce nice error messages (other than "Cannot cast...").
try {
value = DefaultingTy{
pybind11::cast<typename DefaultingTy::ReferrentTy &>(src)};
return true;
} catch (std::exception &) {
return false;
static handle cast(DefaultingTy src, return_value_policy policy,
handle parent) {
return pybind11::cast(src, policy);
template <typename T>
struct type_caster<llvm::Optional<T>> : optional_caster<llvm::Optional<T>> {};
} // namespace detail
} // namespace pybind11
// Conversion utilities.
namespace mlir {
/// Accumulates into a python string from a method that accepts an
/// MlirStringCallback.
struct PyPrintAccumulator {
pybind11::list parts;
void *getUserData() { return this; }
MlirStringCallback getCallback() {
return [](MlirStringRef part, void *userData) {
PyPrintAccumulator *printAccum =
static_cast<PyPrintAccumulator *>(userData);
pybind11::str pyPart(,
part.length); // Decodes as UTF-8 by default.
pybind11::str join() {
pybind11::str delim("", 0);
return delim.attr("join")(parts);
/// Accumulates int a python file-like object, either writing text (default)
/// or binary.
class PyFileAccumulator {
PyFileAccumulator(pybind11::object fileObject, bool binary)
: pyWriteFunction(fileObject.attr("write")), binary(binary) {}
void *getUserData() { return this; }
MlirStringCallback getCallback() {
return [](MlirStringRef part, void *userData) {
PyFileAccumulator *accum = static_cast<PyFileAccumulator *>(userData);
if (accum->binary) {
// Note: Still has to copy and not avoidable with this API.
pybind11::bytes pyBytes(, part.length);
} else {
pybind11::str pyStr(,
part.length); // Decodes as UTF-8 by default.
pybind11::object pyWriteFunction;
bool binary;
/// Accumulates into a python string from a method that is expected to make
/// one (no more, no less) call to the callback (asserts internally on
/// violation).
struct PySinglePartStringAccumulator {
void *getUserData() { return this; }
MlirStringCallback getCallback() {
return [](MlirStringRef part, void *userData) {
PySinglePartStringAccumulator *accum =
static_cast<PySinglePartStringAccumulator *>(userData);
assert(!accum->invoked &&
"PySinglePartStringAccumulator called back multiple times");
accum->invoked = true;
accum->value = pybind11::str(, part.length);
pybind11::str takeValue() {
assert(invoked && "PySinglePartStringAccumulator not called back");
return std::move(value);
pybind11::str value;
bool invoked = false;
/// A CRTP base class for pseudo-containers willing to support Python-type
/// slicing access on top of indexed access. Calling ::bind on this class
/// will define `__len__` as well as `__getitem__` with integer and slice
/// arguments.
/// This is intended for pseudo-containers that can refer to arbitrary slices of
/// underlying storage indexed by a single integer. Indexing those with an
/// integer produces an instance of ElementTy. Indexing those with a slice
/// produces a new instance of Derived, which can be sliced further.
/// A derived class must provide the following:
/// - a `static const char *pyClassName ` field containing the name of the
/// Python class to bind;
/// - an instance method `intptr_t getNumElements()` that returns the number
/// of elements in the backing container (NOT that of the slice);
/// - an instance method `ElementTy getElement(intptr_t)` that returns a
/// single element at the given index.
/// - an instance method `Derived slice(intptr_t, intptr_t, intptr_t)` that
/// constructs a new instance of the derived pseudo-container with the
/// given slice parameters (to be forwarded to the Sliceable constructor).
/// A derived class may additionally define:
/// - a `static void bindDerived(ClassTy &)` method to bind additional methods
/// the python class.
template <typename Derived, typename ElementTy>
class Sliceable {
using ClassTy = pybind11::class_<Derived>;
intptr_t wrapIndex(intptr_t index) {
if (index < 0)
index = length + index;
if (index < 0 || index >= length) {
throw python::SetPyError(PyExc_IndexError,
"attempt to access out of bounds");
return index;
explicit Sliceable(intptr_t startIndex, intptr_t length, intptr_t step)
: startIndex(startIndex), length(length), step(step) {
assert(length >= 0 && "expected non-negative slice length");
/// Returns the length of the slice.
intptr_t dunderLen() const { return length; }
/// Returns the element at the given slice index. Supports negative indices
/// by taking elements in inverse order. Throws if the index is out of bounds.
ElementTy dunderGetItem(intptr_t index) {
// Negative indices mean we count from the end.
index = wrapIndex(index);
// Compute the linear index given the current slice properties.
int linearIndex = index * step + startIndex;
assert(linearIndex >= 0 &&
linearIndex < static_cast<Derived *>(this)->getNumElements() &&
"linear index out of bounds, the slice is ill-formed");
return static_cast<Derived *>(this)->getElement(linearIndex);
/// Returns a new instance of the pseudo-container restricted to the given
/// slice.
Derived dunderGetItemSlice(pybind11::slice slice) {
ssize_t start, stop, extraStep, sliceLength;
if (!slice.compute(dunderLen(), &start, &stop, &extraStep, &sliceLength)) {
throw python::SetPyError(PyExc_IndexError,
"attempt to access out of bounds");
return static_cast<Derived *>(this)->slice(startIndex + start * step,
sliceLength, step * extraStep);
/// Returns a new vector (mapped to Python list) containing elements from two
/// slices. The new vector is necessary because slices may not be contiguous
/// or even come from the same original sequence.
std::vector<ElementTy> dunderAdd(Derived &other) {
std::vector<ElementTy> elements;
elements.reserve(length + other.length);
for (intptr_t i = 0; i < length; ++i) {
for (intptr_t i = 0; i < other.length; ++i) {
return elements;
/// Binds the indexing and length methods in the Python class.
static void bind(pybind11::module &m) {
auto clazz = pybind11::class_<Derived>(m, Derived::pyClassName,
.def("__len__", &Sliceable::dunderLen)
.def("__getitem__", &Sliceable::dunderGetItem)
.def("__getitem__", &Sliceable::dunderGetItemSlice)
.def("__add__", &Sliceable::dunderAdd);
/// Hook for derived classes willing to bind more methods.
static void bindDerived(ClassTy &) {}
intptr_t startIndex;
intptr_t length;
intptr_t step;
} // namespace mlir