Use context manager for writing param_file

lib/galaxy/tools/evaluation.py

@@ -584,14 +584,13 @@ class ToolEvaluator(object):
         if self.tool.profile < 16.04 and command and "$param_file" in command:
             fd, param_filename = tempfile.mkstemp(dir=directory)
             os.close(fd)
-            f = open(param_filename, "w")
-            for key, value in param_dict.items():
-                # parameters can be strings or lists of strings, coerce to list
-                if not isinstance(value, list):
-                    value = [value]
-                for elem in value:
-                    f.write('%s=%s\n' % (key, elem))
-            f.close()
+            with open(param_filename, "w") as f:
+                for key, value in param_dict.items():
+                    # parameters can be strings or lists of strings, coerce to list
+                    if not isinstance(value, list):
+                        value = [value]
+                    for elem in value:
+                        f.write('%s=%s\n' % (key, elem))
             self.__register_extra_file('param_file', param_filename)
             return param_filename
         else: