Soft deps in setup

.coveragerc

@@ -7,6 +7,7 @@ branch = True
 omit = 
     setup.py
     iris_grib/tests/*
+    .eggs/*
 
 
 [report]

iris_grib/_iris_mercator_support.py

@@ -0,0 +1,40 @@
+# (C) British Crown Copyright 2018, Met Office
+#
+# This file is part of iris-grib.
+#
+# iris-grib is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# iris-grib is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with iris-grib.  If not, see <http://www.gnu.org/licenses/>.
+"""
+Temporary module to check for the extended Mercator class in Iris,
+which iris-grib requires for its Mercator support.
+
+"""
+from __future__ import (absolute_import, division, print_function)
+from six.moves import (filter, input, map, range, zip)  # noqa
+import six
+
+import distutils.version
+
+import iris
+
+
+def confirm_extended_mercator_supported():
+    # Check that Iris version is at least 2.1, required for 'standard_parallel'
+    # support in the Mercator coord-system.
+    # This is a temporary fix allowing us to state Iris>=2.0 as a dependency,
+    # required for this release because Iris 2.1 is not yet available.
+    iris_version = distutils.version.LooseVersion(iris.__version__)
+    min_mercator_version = '2.1.0'
+    if iris_version < min_mercator_version:
+        msg = 'Support for Mercator projections requires Iris version >= {}'
+        raise ValueError(msg.format(min_mercator_version))

iris_grib/_load_convert.py

@@ -43,6 +43,7 @@
     ReferenceTarget
 from iris.util import _is_circular
 
+from ._iris_mercator_support import confirm_extended_mercator_supported
 from ._grib1_load_rules import grib1_convert
 from .message import GribMessage
 
@@ -746,6 +747,9 @@ def grid_definition_template_10(section, metadata):
     # intersects the Earth
     standard_parallel = section['LaD'] * _GRID_ACCURACY_IN_DEGREES
 
+    # Check and raise a more intelligible error, if the Iris version is too old
+    # to support the Mercator 'standard_parallel' keyword.
+    confirm_extended_mercator_supported()
     cs = icoord_systems.Mercator(standard_parallel=standard_parallel,
                                  ellipsoid=geog_cs)
 

iris_grib/_save_rules.py

@@ -39,6 +39,7 @@
                                 TransverseMercator, LambertConformal)
 import iris.exceptions
 
+from ._iris_mercator_support import confirm_extended_mercator_supported
 from . import grib_phenom_translation as gptx
 from ._load_convert import (_STATISTIC_TYPE_NAMES, _TIME_RANGE_UNITS)
 from iris.util import is_regular, regular_step
@@ -503,6 +504,9 @@ def grid_definition_template_10(cube, grib):
     gribapi.grib_set(grib, "longitudeOfLastGridPoint",
                      int(np.round(last_x / _DEFAULT_DEGREES_UNITS)))
 
+    # Check and raise a more intelligible error, if the Iris version is too old
+    # to support the Mercator 'standard_parallel' property.
+    confirm_extended_mercator_supported()
     # Encode the latitude at which the projection intersects the Earth.
     gribapi.grib_set(grib, 'LaD',
                      cs.standard_parallel / _DEFAULT_DEGREES_UNITS)

setup.py

@@ -79,10 +79,12 @@ def file_walk_relative(top, remove=''):
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
     ],
-    install_requires = [
-        #        'iris>=1.9,<2',
-        # Also: the ECMWF GRIB API
-    ],
+    # NOTE: This Iris version requirement is a purely temporary measure :
+    # Iris>=2.1 is needed for Mercator support, but this is not yet available,
+    # so 'iris_grib._confirm_iris_mercator_support' performs a runtime version
+    # check instead + raises an error if required.
+    # TODO: update Iris version and remove runtime checking, in future release.
+    install_requires = ['scitools-iris>=2.0.*', 'eccodes'],
     extras_require = {
         'test:python_version=="2.7"': ['mock'],
     },