JSON Serializer for pystencils config

This MR adds a custom JSON serializer to allow pystencils configs to be used as parameters in databases. Useful in parameter studies when using the more modern way of setting up simulations, i.e., using pystencils' CreateKernelConfig.

Can be extended in the future for other custom classes if needed.

pystencils/runhelper/db.py

 import socket
 import time
+from types import MappingProxyType
 from typing import Dict, Iterator, Sequence
 
 import blitzdb
+import six
+from blitzdb.backends.file.backend import serializer_classes
+from blitzdb.backends.file.utils import JsonEncoder
 
 from pystencils.cpu.cpujit import get_compiler_config
+from pystencils import CreateKernelConfig, Target, Backend, Field
+
+import json
+import sympy as sp
+
+from pystencils.typing import BasicType
+
+
+class PystencilsJsonEncoder(JsonEncoder):
+
+    def default(self, obj):
+        if isinstance(obj, CreateKernelConfig):
+            return obj.__dict__
+        if isinstance(obj, (sp.Float, sp.Rational)):
+            return float(obj)
+        if isinstance(obj, sp.Integer):
+            return int(obj)
+        if isinstance(obj, (BasicType, MappingProxyType)):
+            return str(obj)
+        if isinstance(obj, (Target, Backend, sp.Symbol)):
+            return obj.name
+        if isinstance(obj, Field):
+            return f"pystencils.Field(name = {obj.name}, field_type = {obj.field_type.name}, " \
+                   f"dtype = {str(obj.dtype)}, layout = {obj.layout}, shape = {obj.shape}, " \
+                   f"strides = {obj.strides})"
+        return JsonEncoder.default(self, obj)
+
+
+class PystencilsJsonSerializer(object):
+
+    @classmethod
+    def serialize(cls, data):
+        if six.PY3:
+            if isinstance(data, bytes):
+                return json.dumps(data.decode('utf-8'), cls=PystencilsJsonEncoder, ensure_ascii=False).encode('utf-8')
+            else:
+                return json.dumps(data, cls=PystencilsJsonEncoder, ensure_ascii=False).encode('utf-8')
+        else:
+            return json.dumps(data, cls=PystencilsJsonEncoder, ensure_ascii=False).encode('utf-8')
+
+    @classmethod
+    def deserialize(cls, data):
+        if six.PY3:
+            return json.loads(data.decode('utf-8'))
+        else:
+            return json.loads(data.decode('utf-8'))
 
 
 class Database:
@@ -46,7 +96,7 @@ class Database:
     class SimulationResult(blitzdb.Document):
         pass
 
-    def __init__(self, file: str) -> None:
+    def __init__(self, file: str, serializer_info: tuple = None) -> None:
         if file.startswith("mongo://"):
             from pymongo import MongoClient
             db_name = file[len("mongo://"):]
@@ -57,6 +107,10 @@ class Database:
 
         self.backend.autocommit = True
 
+        if serializer_info:
+            serializer_classes.update({serializer_info[0]: serializer_info[1]})
+            self.backend.load_config({'serializer_class': serializer_info[0]}, True)
+
     def save(self, params: Dict, result: Dict, env: Dict = None, **kwargs) -> None:
         """Stores a simulation result in the database.
 
@@ -146,10 +200,15 @@ class Database:
             'cpuCompilerConfig': get_compiler_config(),
         }
         try:
-            from git import Repo, InvalidGitRepositoryError
+            from git import Repo
+        except ImportError:
+            return result
+
+        try:
+            from git import InvalidGitRepositoryError
             repo = Repo(search_parent_directories=True)
             result['git_hash'] = str(repo.head.commit)
-        except (ImportError, InvalidGitRepositoryError):
+        except InvalidGitRepositoryError:
             pass
 
         return result