API: remove functions that need diffpy.structure.

Drop `crystalToDiffpyStructure` and `expandSymmetry` as they are
very old and hardly ever used.  Avoid dependency on diffpy.structure.

Author: pavoljuhas

src/pyobjcryst/utils.py

@@ -15,53 +15,6 @@
 
 """Utilities for crystals."""
 
-def crystalToDiffpyStructure(crystal):
-    """Create a diffpy.Structure.Structure from a crystal.
-
-    This requires diffpy.Structure to be installed. This uses file IO transfer
-    data, so there is some inherent precision loss.
-
-    Note that the resulting structure will be in P1 symmetry.
-
-    """
-
-    # Write the crystal to string and load it into a diffpy Structure
-
-    from io import StringIO
-    buf = StringIO()
-    crystal.CIFOutput(buf)
-
-    from diffpy.Structure import Structure
-    stru = Structure()
-
-    s = buf.getvalue()
-    stru.readStr(s)
-    buf.close()
-
-    return stru
-
-def expandSymmetry(crystal):
-    """Expand a crystal to P1 symmetry.
-
-    This requires diffpy.Structure to be installed. This uses file IO transfer
-    data, so there is some inherent precision loss.
-
-    This returns a new structure.
-
-    """
-
-    # Create a string from a diffpy Structure, which is in P1 symmetry, and
-    # load this as a Crystal.
-    stru = crystalToDiffpyStructure(crystal)
-
-    cifstr = stru.writeStr(format = "cif")
-    from io import StringIO
-    buf = StringIO(cifstr)
-
-    from pyobjcryst.crystal import CreateCrystalFromCIF
-    p1 = CreateCrystalFromCIF(buf)
-    return p1
-
 
 def putAtomsInMolecule(crystal, alist = None, name = None):
     """Place atoms from a crystal into a molecule inside the crystal.