Mol2 universe (#2718)

* Fixes issue 2717

* Adds tests

* Switched ag safeguard to encode_block

package/CHANGELOG

@@ -23,6 +23,7 @@ mm/dd/yy richardjgowers, kain88-de, lilyminium, p-j-smith, bdice, joaomcteixeira
   * 0.21.0
 
 Fixes
+  * MOL2Writer now accepts both Universes and AtomgGroups (Issue #2717)
   * Use user-provided `remark` in `XYZWriter` (Issue #2692)
   * Added more informative error messages about topology attributes
     (Issue #2565)

package/MDAnalysis/coordinates/MOL2.py

@@ -306,6 +306,8 @@ def encode_block(self, obj):
         ----------
         obj : AtomGroup or Universe
         """
+        # Issue 2717
+        obj = obj.atoms
         traj = obj.universe.trajectory
         ts = traj.ts
 

testsuite/MDAnalysisTests/coordinates/test_mol2.py

@@ -29,6 +29,7 @@
 from numpy.testing import (
     assert_equal, assert_array_equal,
     assert_array_almost_equal, TestCase,
+    assert_almost_equal
 )
 
 from MDAnalysisTests.datafiles import (
@@ -190,3 +191,19 @@ def test_mol2_multi_write(tmpdir):
         u = mda.Universe(mol2_molecules)
         u.atoms[:4].write('group1.mol2')
         u.atoms[:4].write('group1.mol2')
+
+
+def test_mol2_universe_write(tmpdir):
+    # see Issue 2717
+    with tmpdir.as_cwd():
+        outfile = 'test.mol2'
+
+        u = mda.Universe(mol2_comments_header)
+
+        with mda.Writer(outfile) as W:
+            W.write(u)
+
+        u2 = mda.Universe(outfile)
+
+        assert_almost_equal(u.atoms.positions, u2.atoms.positions)
+        assert_almost_equal(u.dimensions, u2.dimensions)