debian/changelog

+pywps (4.2.1-3) unstable; urgency=medium
+
+  * Add Breaks/Replaces to fix upgrade to python3-pywps.
+
+ -- Bas Couwenberg <sebastic@debian.org>  Sat, 14 Sep 2019 07:47:13 +0200
+
 pywps (4.2.1-2) unstable; urgency=medium
 
   * Update gbp.conf to use --source-only-changes by default.

debian/control

@@ -47,6 +47,8 @@ Recommends: python3-mapscript,
             python3-pyproj
 Suggests: grass-core,
           r-base
+Breaks: python-pywps (<< 4.2.1-2~)
+Replaces: python-pywps (<< 4.2.1-2~)
 Description: Implementation of OGC's Web Processing Service - Python module
  PyWPS is implementation of Web Processing Service from Open
  Geospatial Consortium Inc.(R) with help of  Python Programming