Handle schedules too

This commit updates the schedule serialization path too, as it was also
directly loading symengine expressions. The code handling the workaround
is extracted to a standalone function which is used in both spots now
instead of calling symengine directly.

qiskit/qpy/binary_io/schedules.py

@@ -106,7 +106,7 @@ def _loads_symbolic_expr(expr_bytes, use_symengine=False):
         return None
     expr_bytes = zlib.decompress(expr_bytes)
     if use_symengine:
-        return load_basic(expr_bytes)
+        return common.load_symengine_payload(expr_bytes)
     else:
         from sympy import parse_expr
 

qiskit/qpy/binary_io/value.py

@@ -290,30 +290,7 @@ def _read_parameter_expression_v3(file_obj, vectors, use_symengine):
 
     payload = file_obj.read(data.expr_size)
     if use_symengine:
-        # This is a horrible hack to workaround the symengine version checking
-        # it's deserialization does. There were no changes to the serialization
-        # format between 0.11 and 0.13 but the deserializer checks that it can't
-        # load across a major or minor version boundary. This works around it
-        # by just lying about the generating version.
-        symengine_version = symengine.__version__.split(".")
-        major = payload[2]
-        minor = payload[3]
-        if int(symengine_version[1]) != minor:
-            if minor not in (11, 13):
-                raise exceptions.QpyError(
-                    f"Incompatible symengine version {major}.{minor} used to generate the QPY "
-                    "payload"
-                )
-            minor_version = int(symengine_version[1])
-            if minor_version not in (11, 13):
-                raise exceptions.QpyError(
-                    f"Incompatible installed symengine version {symengine.__version__} to load "
-                    "this QPY payload"
-                )
-            payload = bytearray(payload)
-            payload[3] = minor_version
-            payload = bytes(payload)
-        expr_ = load_basic(payload)
+        expr_ = common.load_symengine_payload(payload)
     else:
         from sympy.parsing.sympy_parser import parse_expr
 

qiskit/qpy/common.py

@@ -18,7 +18,12 @@
 import io
 import struct
 
-from qiskit.qpy import formats
+import symengine
+from symengine.lib.symengine_wrapper import (  # pylint: disable = no-name-in-module
+    load_basic,
+)
+
+from qiskit.qpy import formats, exceptions
 
 QPY_VERSION = 12
 QPY_COMPATIBILITY_VERSION = 10
@@ -304,3 +309,31 @@ def mapping_from_binary(binary_data, deserializer, **kwargs):
         mapping = read_mapping(container, deserializer, **kwargs)
 
     return mapping
+
+
+def load_symengine_payload(payload: bytes) -> symengine.Expr:
+    """Load a symengine expression from it's serialized cereal payload."""
+    # This is a horrible hack to workaround the symengine version checking
+    # it's deserialization does. There were no changes to the serialization
+    # format between 0.11 and 0.13 but the deserializer checks that it can't
+    # load across a major or minor version boundary. This works around it
+    # by just lying about the generating version.
+    symengine_version = symengine.__version__.split(".")
+    major = payload[2]
+    minor = payload[3]
+    if int(symengine_version[1]) != minor:
+        if minor not in (11, 13):
+            raise exceptions.QpyError(
+                f"Incompatible symengine version {major}.{minor} used to generate the QPY "
+                "payload"
+            )
+        minor_version = int(symengine_version[1])
+        if minor_version not in (11, 13):
+            raise exceptions.QpyError(
+                f"Incompatible installed symengine version {symengine.__version__} to load "
+                "this QPY payload"
+            )
+        payload = bytearray(payload)
+        payload[3] = minor_version
+        payload = bytes(payload)
+    return load_basic(payload)