Fix missing import in gravimetry

Because cwrapped functions need classes to be defined for
all of their inputs, we need to import them.

Added type hints to avoid linters complaining about unused
imports.

python/ecl/gravimetry/ecl_grav.py

@@ -6,12 +6,15 @@
 different surveys. The implementation is a thin wrapper around the
 ecl_grav.c implementation in the libecl library.
 """
+from typing import Optional
+
 from cwrap import BaseCClass
 
 from ecl import EclPrototype
+from ecl.grid import EclGrid, EclRegion
+from ecl.eclfile import EclFileView, EclFile
 from ecl.util.util import monkey_the_camel
 from ecl import EclPhaseEnum
-import ecl.eclfile
 
 
 class EclGrav(BaseCClass):
@@ -56,12 +59,9 @@ class is focused on the ECLIPSE side of things, and does not have
         "double ecl_grav_eval(ecl_grav, char*, char*, ecl_region, double, double, double, int)"
     )
 
-    def __init__(self, grid, init_file):
+    def __init__(self, grid: EclGrid, init_file: EclFile):
         """
         Creates a new EclGrav instance.
-
-        The input arguments @grid and @init_file should be instances
-        of EclGrid and EclFile respectively.
         """
         self.init_file = init_file  # Inhibit premature garbage collection of init_file
 
@@ -75,7 +75,7 @@ def __init__(self, grid, init_file):
             "RPORV": self.add_survey_RPORV,
         }
 
-    def add_survey_RPORV(self, survey_name, restart_view):
+    def add_survey_RPORV(self, survey_name: str, restart_view: EclFileView):
         """
         Add new survey based on RPORV keyword.
 
@@ -87,11 +87,11 @@ def add_survey_RPORV(self, survey_name, restart_view):
         to load the @restart_view argument is:
 
            import datetime
-           from ecl.ecl import EclRestartFile
+           from ecl.eclfile import EclFile
            ...
            ...
            date = datetime.datetime(year, month, day)
-           rst_file = EclRestartFile("ECLIPSE.UNRST")
+           rst_file = EclFile("ECLIPSE.UNRST")
            restart_view1 = rst_file.restartView(sim_time=date)
            restart_view2 = rst_file.restartView(report_step=67)
 
@@ -102,7 +102,7 @@ def add_survey_RPORV(self, survey_name, restart_view):
         """
         self._add_survey_RPORV(survey_name, restart_view)
 
-    def add_survey_PORMOD(self, survey_name, restart_view):
+    def add_survey_PORMOD(self, survey_name: str, restart_view: EclFileView):
         """
         Add new survey based on PORMOD keyword.
 
@@ -112,7 +112,7 @@ def add_survey_PORMOD(self, survey_name, restart_view):
         """
         self._add_survey_PORMOD(survey_name, restart_view)
 
-    def add_survey_FIP(self, survey_name, restart_view):
+    def add_survey_FIP(self, survey_name: str, restart_view: EclFileView):
         """
         Add new survey based on FIP keywords.
 
@@ -127,7 +127,7 @@ def add_survey_FIP(self, survey_name, restart_view):
         """
         self._add_survey_FIP(survey_name, restart_view)
 
-    def add_survey_RFIP(self, survey_name, restart_view):
+    def add_survey_RFIP(self, survey_name: str, restart_view: EclFileView):
         """
         Add new survey based on RFIP keywords.
 
@@ -138,7 +138,7 @@ def add_survey_RFIP(self, survey_name, restart_view):
         """
         self._add_survey_RFIP(survey_name, restart_view)
 
-    def add_survey(self, name, restart_view, method):
+    def add_survey(self, name: str, restart_view: EclFileView, method):
         method = self.dispatch[method]
         return method(name, restart_view)
 
@@ -147,7 +147,7 @@ def eval(
         base_survey,
         monitor_survey,
         pos,
-        region=None,
+        region: Optional[EclRegion]=None,
         phase_mask=EclPhaseEnum.ECL_OIL_PHASE
         + EclPhaseEnum.ECL_GAS_PHASE
         + EclPhaseEnum.ECL_WATER_PHASE,