Catch ImportWarning when compiling or loading cython string co-effici…

…ents for Python 3.10.

qutip/core/coefficient.py

@@ -8,8 +8,7 @@
 import hashlib
 import glob
 import importlib
-import inspect
-import shutil
+import warnings
 import numbers
 from contextlib import contextmanager
 from collections import defaultdict
@@ -18,7 +17,6 @@
     from Cython.Build import cythonize
 except ImportError:
     pass
-from warnings import warn
 
 from ..settings import settings as qset
 from ..optionsclass import optionsclass
@@ -33,6 +31,17 @@
            "clean_compiled_coefficient"]
 
 
+@contextmanager
+def _ignore_import_warning_for_pyximporter():
+    """
+    A helper for ignoring PyxImporter import warnings generated by Python 3.10+
+    because PyxImporter has no .find_spec method.
+    """
+    with warnings.catch_warnings():
+        warnings.filterwarnings("ignore", category=ImportWarning)
+        yield
+
+
 class StringParsingWarning(Warning):
     pass
 
@@ -348,9 +357,9 @@ def try_import(file_name, parsed_in):
     name collision.
     """
     get_root()
-    coeff = None
     try:
-        mod = importlib.import_module(file_name)
+        with _ignore_import_warning_for_pyximporter():
+            mod = importlib.import_module(file_name)
     except ModuleNotFoundError:
         # Coefficient does not exist, to compile as file_name
         return None
@@ -486,7 +495,9 @@ def compile_code(code, file_name, parsed, c_opt):
                 include_dirs=[np.get_include()],
                 language='c++'
             )
-            setup(ext_modules=cythonize(coeff_file, force=c_opt['recompile']))
+            with _ignore_import_warning_for_pyximporter():
+                ext_modules = cythonize(coeff_file, force=c_opt['recompile'])
+                setup(ext_modules=ext_modules)
         except Exception as e:
             raise Exception("Could not compile") from e
         finally:
@@ -691,7 +702,7 @@ def try_parse(code, args, args_ctypes, compile_opt):
     ):
         return ncode, variables, constants, False
     else:
-        warn("Could not find c types", StringParsingWarning)
+        warnings.warn("Could not find c types", StringParsingWarning)
         remaped_variable = []
         for _, name, ctype in variables:
             remaped_variable.append(("self." + name, name, "object"))