silence duecredit import failure

- fix #1872
- Do not show a warning if duecredit is not installed;
  if users want the functionality they can install duecredit
  but we should not bother all others.
- NOTE: This was manually tested in a local installation without
        duecredit but doing a real unit test is difficult and
        has not been attempted.

package/CHANGELOG

@@ -13,7 +13,7 @@ The rules for this file:
   * release numbers follow "Semantic Versioning" http://semver.org
 
 ------------------------------------------------------------------------------
-??/??/18 richardjgowers, palnabarun
+??/??/18 richardjgowers, palnabarun, orbeckst
 
   * 0.18.1
 
@@ -22,7 +22,8 @@ Enhancements
 Fixes
   * Fixed order of indices in Angle/Dihedral/Improper repr
   * coordinates.memory.MemoryReader now takes np.ndarray only (Issue #1685)
-
+  * Silenced warning when duecredit is not installed (Issue #1872)
+
 Changes
 
 

package/MDAnalysis/due.py

@@ -82,10 +82,10 @@ def _donothing_func(*args, **kwargs):
         warnings.warn(errmsg)
         logging.getLogger("duecredit").error(
             "Failed to import duecredit due to {}".format(str(err)))
-    else:
-        # for debugging
-        import warnings
-        warnings.warn(str(err))
+    # else:
+    #   Do not issue any warnings if duecredit is not installed;
+    #   this is the user's choice (Issue #1872)
+
     # Initiate due stub
     due = InactiveDueCreditCollector()
     BibTeX = Doi = Url = _donothing_func