support pybind v2.2

We were seeing multiple deprecation warnings when compiling NMSLIB against the newest release
of pybind11 (v2.2.1). This patch fixes so that python_bindings/nmslib.cc will build without
warnings with pybind11 v2.2.1.

Also we were claiming support for pybind v2.0.0 - but there are build errors when compiling
against that version. Support this by using mutable_at instead of mutable_unchecked etc.

python_bindings/nmslib.cc

@@ -149,14 +149,12 @@ struct IndexWrapper {
     size_t size = res->Size();
     py::array_t<int> ids(size);
     py::array_t<dist_t> distances(size);
-    auto raw_ids = ids.mutable_unchecked();
-    auto raw_distances = distances.mutable_unchecked();
 
     while (!res->Empty() && size > 0) {
       // iterating here in reversed order, undo that
       size -= 1;
-      raw_ids(size) = res->TopObject()->id();
-      raw_distances(size) = res->TopDistance();
+      ids.mutable_at(size) = res->TopObject()->id();
+      distances.mutable_at(size) = res->TopDistance();
       res->Pop();
     }
     return py::make_tuple(ids, distances);
@@ -195,7 +193,7 @@ struct IndexWrapper {
   size_t readObjectVector(py::object input, ObjectVector * output,
                           py::object ids_ = py::none()) {
     std::vector<int> ids;
-    if (ids_ != py::none()) {
+    if (!ids_) {
       ids = py::cast<std::vector<int>>(ids_);
     }
 
@@ -234,10 +232,10 @@ struct IndexWrapper {
       // read each row from the sparse matrix, and insert
       auto sparse_space = reinterpret_cast<const SpaceSparseVector<dist_t>*>(space.get());
       std::vector<SparseVectElem<dist_t>> sparse_items;
-      for (size_t rowid = 0; rowid < indptr.size() - 1; ++rowid) {
+      for (int rowid = 0; rowid < indptr.size() - 1; ++rowid) {
         sparse_items.clear();
 
-        for (size_t i = indptr.at(rowid); i < indptr.at(rowid + 1); ++i) {
+        for (int i = indptr.at(rowid); i < indptr.at(rowid + 1); ++i) {
           sparse_items.push_back(SparseVectElem<dist_t>(indices.at(i),
                                  sparse_data.at(i)));
         }
@@ -352,15 +350,20 @@ class PythonLogger
   }
 };
 
+#ifdef PYBIND11_MODULE
+PYBIND11_MODULE(nmslib, m) {
+  m.doc() = "Python Bindings for Non-Metric Space Library (NMSLIB)";
+#else
 PYBIND11_PLUGIN(nmslib) {
+  py::module m(module_name, "Python Bindings for Non-Metric Space Library (NMSLIB)");
+#endif
   // Log using the python logger, instead of defaults built in here
   py::module logging = py::module::import("logging");
   py::module nmslibLogger = logging.attr("getLogger")("nmslib");
   setGlobalLogger(new PythonLogger(nmslibLogger));
 
   initLibrary(0 /* seed */, LIB_LOGCUSTOM, NULL);
 
-  py::module m(module_name, "Bindings for Non-Metric Space Library (NMSLIB)");
 
 #ifdef VERSION_INFO
   m.attr("__version__") = py::str(VERSION_INFO);
@@ -438,7 +441,10 @@ PYBIND11_PLUGIN(nmslib) {
   exportIndex<double>(&dist_module);
 
   exportLegacyAPI(&m);
+
+#ifndef PYBIND11_MODULE
   return m.ptr();
+#endif
 }
 
 template <typename dist_t>
@@ -583,7 +589,7 @@ AnyParams loadParams(py::object o) {
   if (py::isinstance<py::dict>(o)) {
     AnyParams ret;
     py::dict items(o);
-    for (auto & item : items) {
+    for (auto item : items) {
       std::string key = py::cast<std::string>(item.first);
       auto & value = item.second;