addressed comments by @IAlibay and @tluchko

- add versionchanged noting use of MRC instead of CCP4
- add undocumented Grid._mrc_header for storing the MRC header
- add tests (for _mrc_header and generally checking that a correct
  Grid object is built from the MRC data)
- code/doc cleanup

gridData/CCP4.py

@@ -164,6 +164,7 @@ class CCP4(object):
        * index ordering besides standard column-major and row-major
        * non-standard fields, such any in filed in future use block
 
+
     .. deprecated:: 0.7.0
        Use :class:`gridData.mrc.MRC` instead. This class will be removed in 0.8.0.
     """

gridData/core.py

@@ -114,6 +114,10 @@ def __init__(self, grid=None, edges=None, origin=None, delta=None,
         .. versionchanged:: 0.5.0
            New *file_format* keyword argument.
 
+        .. versionchanged:: 0.7.0
+           CCP4 files are now read with :class:`gridData.mrc.MRC` and not anymore
+           with the deprecated/buggy `ccp4.CCP4`
+
         """
         # file formats are guess from extension == lower case key
         self._exporters = {
@@ -477,6 +481,9 @@ def _load_mrc(self, filename):
         mrcfile = mrc.MRC(filename)
         grid, edges = mrcfile.histogramdd()
         self._load(grid=grid, edges=edges, metadata=self.metadata)
+        # Store header for access from Grid object (undocumented)
+        # https://github.com/MDAnalysis/GridDataFormats/pull/100#discussion_r782604833
+        self._mrc_header = mrcfile.header.copy()
 
     def _load_dx(self, filename):
         """Initializes Grid from a OpenDX file."""

gridData/mrc.py

@@ -34,8 +34,6 @@
 from __future__ import absolute_import
 from six.moves import range
 
-import warnings
-
 import numpy as np
 import mrcfile
 

gridData/tests/test_mrc.py

@@ -115,3 +115,23 @@ def test_triclinic_ValueError():
                        "supported, not"):
         Grid(datafiles.MRC_EMD3001, file_format="MRC")
 
+class TestGridMRC():
+    @pytest.fixture(scope="class")
+    def grid(self):
+        return Grid(datafiles.CCP4_1JZV)
+
+    def test_shape(self, grid, ccp4data):
+        assert_equal(grid.grid.shape, ccp4data.shape)
+
+    def test_mrc_header(self, grid, ccp4data):
+        # undocumented MRC header in Grid
+        assert grid._mrc_header == ccp4data.header
+
+    def test_delta(self, grid, ccp4data):
+        assert_almost_equal(grid.delta, np.diag(ccp4data.delta))
+
+    def test_origin(self, grid, ccp4data):
+        assert_almost_equal(grid.origin, ccp4data.origin)
+
+    def test_data(self, grid, ccp4data):
+        assert_almost_equal(grid.grid, ccp4data.array)