Ignore new entrypoints when using old versions of the driver (#5)

* Ignore new entrypoints when using old versions of the driver

Allow the Python API to work with existing versions of the driver as we
add new entrypoints to the API.  New functions throw a Version Mismatch
error if used on a driver that doesn't support them.

* Removing excess whitespace

nifpga/statuscheckedlibrary.py

@@ -1,4 +1,4 @@
-from .status import check_status
+from .status import check_status, VersionMismatchError
 import ctypes
 import ctypes.util
 
@@ -176,14 +176,22 @@ def __init__(self, library_name, library_function_infos):
         library = ctypes.cdll.LoadLibrary(library)
         function_infos = []
         for lfi in library_function_infos:
-            func = getattr(library, lfi.name_in_library)  # i.e., dlsym()
-            # ctypes functions have special 'argtypes' and 'restype' fields
-            # that we set, so ctypes can automatically convert types and knows
-            # how to call into the library.
-            func.argtypes = [named_argtype.argtype for named_argtype in lfi.named_argtypes]
-            # Assume that everything returns an NiFpga_Status
-            func.restype = StatusType
-
+            try:
+                func = getattr(library, lfi.name_in_library)  # i.e., dlsym()
+                # ctypes functions have special 'argtypes' and 'restype' fields
+                # that we set, so ctypes can automatically convert types and knows
+                # how to call into the library.
+                func.argtypes = [named_argtype.argtype for named_argtype in lfi.named_argtypes]
+                # Assume that everything returns an NiFpga_Status
+                func.restype = StatusType
+            except AttributeError:
+                # if we can't find the symbol, instead insert a function that
+                # always returns the VersionMismatch error, that way they can
+                # use the rest of the API
+                def returnsVersionMismatchError(*args, **kwargs):
+                    """ Always returns the version mismatch error code. """
+                    return VersionMismatchError.CODE
+                func = returnsVersionMismatchError
             function_infos.append(
                 FunctionInfo(function=func,
                              name=lfi.pretty_name,

nifpga/tests/test_nifpga.py

@@ -182,6 +182,32 @@ def test_get_unknown_warning(self):
                 self.assertIn("nptr: b'1'", str(warning))
 
 
+class StatusCheckedLibraryTestFunctionDoesntExist(unittest.TestCase):
+    """
+    New versions of NiFpga will have new functions.  We want the API to support
+    old versions of NiFpga without erroring because it can't find certain symbols.
+    So StatusCheckedLibrary will return FeatureNotSupported for symbols it can't
+    find.
+    """
+    def setUp(self):
+        self._c_runtime = StatusCheckedLibrary(
+            "c",
+            library_function_infos=[
+                LibraryFunctionInfo(
+                    pretty_name="DoesntExist",
+                    name_in_library="functionThatDoesntExist",
+                    named_argtypes=[
+                        NamedArgtype("nptr", ctypes.c_char_p),
+                    ])
+            ])
+
+    def test_correct_error(self):
+        with self.assertRaises(nifpga.VersionMismatchError):
+            self._c_runtime.DoesntExist(b"0")
+        with self.assertRaises(nifpga.VersionMismatchError):
+            self._c_runtime["DoesntExist"](b"0")
+
+
 class StatusCheckedLibraryTestMockedLibrary(unittest.TestCase):
     """
     Since we can't load NiFpga on a dev machine unless we have all its