Add Priority constants

It'd be cool if we could just use org.scijava.priority.Priority, but we
can't do that without pulling in all of SJC. We could get some good use
out of SciJava3 having a SciJava Priority module :)

Author: gselzer

scyjava/__init__.py

@@ -175,11 +175,25 @@ def compare_version(version, java_class_version):
 
 # -- Type Conversion Utilities --
 
+# TODO: It would be cool to just use org.scijava.priority.Priority.
+# Unfortunately, we cannot do that without bringing in all of SJC.
+# Once SciJava 3 is mainstream, we could use a SciJava Priority module :)
+class Priority:
+    FIRST = 1E300
+    EXTREMELY_HIGH = 1E6
+    VERY_HIGH = 1E4
+    HIGH = 1E2
+    NORMAL = 0
+    LOW = -1E2
+    VERY_LOW = -1E4
+    EXTREMELY_LOW = -1E6
+    LAST = -1E300
 
 class Converter(NamedTuple):
     predicate: Callable[[Any], bool]
     converter: Callable[[Any], Any]
-    priority: float
+    # Corresponds with Priority.NORMAL
+    priority: float = 0
 
 
 def _convert(obj: Any, converters: typing.List[Converter]) -> Any:
@@ -296,6 +310,13 @@ def convertIterable(obj: collections.abc.Iterable):
 
 
 def add_java_converter(predicate: Callable[[Any], bool], converter: Callable[[Any], Any], priority: float):
+    """
+    Adds a converter to the list used by to_java
+    :param predicate: A Callable identifying suitable data types for this converter
+    :param converter: A Callable able to convert a set of types
+    :priority: 
+
+    """
     c = Converter(predicate, converter, priority)
     _add_converter(c, java_converters)
 
@@ -325,91 +346,91 @@ def _stock_java_converters() -> typing.List[Converter]:
         Converter(
             predicate=lambda obj: True,
             converter=_raise_type_exception,
-            priority=-10001
+            priority=Priority.EXTREMELY_LOW - 1
         ),
         # NoneType converter
         Converter(
             predicate=lambda obj: obj is None,
             converter=lambda obj: None,
-            priority=10001
+            priority=Priority.EXTREMELY_HIGH + 1
         ),
         # Java identity converter
         Converter(
             predicate=isjava,
             converter=lambda obj: obj,
-            priority=10000
+            priority=Priority.EXTREMELY_HIGH
         ),
         # String converter
         Converter(
             predicate=lambda obj: isinstance(obj, str), 
             converter=lambda obj: String(obj.encode('utf-8'), 'utf-8'),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Boolean converter
         Converter(
             predicate=lambda obj: isinstance(obj, bool),
             converter=Boolean,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Integer converter
         Converter(
             predicate=lambda obj: isinstance(obj, int) and obj <= Integer.MAX_VALUE and obj >= Integer.MIN_VALUE,
             converter= Integer,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Long converter
         Converter(
             predicate=lambda obj: isinstance(obj, int) and obj <= Long.MAX_VALUE,
             converter=Long,
-            priority=-1
+            priority=Priority.NORMAL - 1
         ),
         # BigInteger converter
         Converter(
             predicate=lambda obj: isinstance(obj, int),
             converter=lambda obj: BigInteger(str(obj)),
-            priority=-2
+            priority=Priority.NORMAL - 2
         ),
         # Float converter
         Converter(
             predicate=lambda obj: isinstance(obj, float) and obj <= Float.MAX_VALUE and obj >= Float.MIN_VALUE,
             converter= Float,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Double converter
         Converter(
             predicate=lambda obj: isinstance(obj, float) and obj <= Double.MAX_VALUE and obj >= Float.MIN_VALUE,
             converter=Double,
-            priority=-1
+            priority=Priority.NORMAL - 1
         ),
         # BigDecimal converter
         Converter(
             predicate=lambda obj: isinstance(obj, float),
             converter=lambda obj: BigDecimal(str(obj)),
-            priority=-2
+            priority=Priority.NORMAL - 2
         ),
         # Pandas table converter
         Converter(
             predicate=lambda obj: type(obj).__name__ == 'DataFrame',
             converter=_pandas_to_table,
-            priority=1
+            priority=Priority.NORMAL + 1
         ),
         # Mapping converter
         Converter(
             predicate=lambda obj: isinstance(obj, collections.abc.Mapping),
             converter=convertMap,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Set converter
         Converter(
             predicate=lambda obj: isinstance(obj, collections.abc.Set),
             converter=convertSet,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Iterable converter
         Converter(
             predicate=lambda obj: isinstance(obj, collections.abc.Iterable),
             converter=convertIterable,
-            priority=-1
+            priority=Priority.NORMAL -1
         ),
     ]
 
@@ -623,151 +644,151 @@ def _stock_py_converters() -> typing.List:
         Converter(
             predicate=lambda obj: True,
             converter=_raise_type_exception,
-            priority=-10001
+            priority=Priority.EXTREMELY_LOW - 1
         ),
         # Java identity converter
         Converter(
             predicate=lambda obj: not isjava(obj),
             converter=lambda obj: obj,
-            priority=10000
+            priority=Priority.EXTREMELY_HIGH
         ),
         # JBoolean converter
         Converter(
             predicate=lambda obj: isinstance(obj, JBoolean),
             converter=bool,
-            priority=1
+            priority=Priority.NORMAL + 1
         ),
         # JInt/JLong/JShort converter
         Converter(
             predicate=lambda obj: isinstance(obj, (JInt, JLong, JShort)),
             converter=int,
-            priority=1
+            priority=Priority.NORMAL + 1
         ),
         # JDouble/JFloat converter
         Converter(
             predicate=lambda obj: isinstance(obj, (JDouble, JFloat)),
             converter=float,
-            priority=1
+            priority=Priority.NORMAL + 1
         ),
         # JChar converter
         Converter(
             predicate=lambda obj: isinstance(obj, JChar),
             converter=str,
-            priority=1
+            priority=Priority.NORMAL + 1
         ),
         # Boolean converter
         Converter(
             predicate=lambda obj: isinstance(obj, Boolean),
             converter=lambda obj: obj.booleanValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Byte converter
         Converter(
             predicate=lambda obj: isinstance(obj, Byte),
             converter=lambda obj: obj.byteValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Char converter
         Converter(
             predicate=lambda obj: isinstance(obj, Character),
             converter=lambda obj: obj.toString(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Double converter
         Converter(
             predicate=lambda obj: isinstance(obj, Double),
             converter=lambda obj: obj.doubleValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Float converter
         Converter(
             predicate=lambda obj: isinstance(obj, Float),
             converter=lambda obj: obj.floatValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Integer converter
         Converter(
             predicate=lambda obj: isinstance(obj, Integer),
             converter=lambda obj: obj.intValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Long converter
         Converter(
             predicate=lambda obj: isinstance(obj, Long),
             converter=lambda obj: obj.longValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Short converter
         Converter(
             predicate=lambda obj: isinstance(obj, Short),
             converter=lambda obj: obj.shortValue(),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Void converter
         Converter(
             predicate=lambda obj: isinstance(obj, Void),
             converter=lambda obj: None,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # String converter
         Converter(
             predicate=lambda obj: isinstance(obj, String), 
             converter=lambda obj: str(obj),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # BigInteger converter
         Converter(
             predicate=lambda obj: isinstance(obj, BigInteger),
             converter=lambda obj: int(str(obj.toString())),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # BigDecimal converter
         Converter(
             predicate=lambda obj: isinstance(obj, BigDecimal),
             converter=lambda obj: float(obj.toString),
-            priority=0
+            priority=Priority.NORMAL
         ),
         # SciJava Table converter
         Converter(
             predicate=_is_table,
             converter=_convert_table,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # List converter
         Converter(
             predicate=lambda obj: isinstance(obj, List),
             converter=JavaList,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Map converter
         Converter(
             predicate=lambda obj: isinstance(obj, Map),
             converter=JavaMap,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Set converter
         Converter(
             predicate=lambda obj: isinstance(obj, Set),
             converter=JavaSet,
-            priority=0
+            priority=Priority.NORMAL
         ),
         # Collection converter
         Converter(
             predicate=lambda obj: isinstance(obj, Collection),
             converter=JavaCollection,
-            priority=-1
+            priority=Priority.NORMAL -1
         ),
         # Iterable converter
         Converter(
             predicate=lambda obj: isinstance(obj, Iterable),
             converter=JavaIterable,
-            priority=-1
+            priority=Priority.NORMAL -1
         ),
         # Iterator converter
         Converter(
             predicate=lambda obj: isinstance(obj, Iterator),
             converter=JavaIterator,
-            priority=-1
+            priority=Priority.NORMAL - 1
         ),
     ]