allow selecting a list of timesteps. avoid redundant code

tools/python/pizza/dump.py

@@ -38,6 +38,7 @@ d.map(1,"id",3,"x")               assign names to atom columns (1-N)
 
 d.tselect.all()                   select all timesteps
 d.tselect.one(N)                  select only timestep N
+d.tselect.one(N1,N2,N3)           select only timestep N1,N2,N3
 d.tselect.none()                  deselect all timesteps
 d.tselect.skip(M)                 select every Mth step
 d.tselect.test("$t >= 100 and $t < 10000")      select matching timesteps
@@ -1117,24 +1118,23 @@ class tselect:
 
   # --------------------------------------------------------------------
 
-  def one(self,n):
+  def one(self,*steps):
     data = self.data
+    data.nselect = 0
     for snap in data.snaps:
       snap.tselect = 0
+
+    for n in steps:
       i = data.findtime(n)
       data.snaps[i].tselect = 1
-    data.nselect = 1
+      data.nselect += 1
       data.aselect.all()
     print("%d snapshots selected out of %d" % (data.nselect,data.nsnaps))
 
   # --------------------------------------------------------------------
 
   def none(self):
-    data = self.data
-    for snap in data.snaps:
-      snap.tselect = 0
-    data.nselect = 0
-    print("%d snapshots selected out of %d" % (data.nselect,data.nsnaps))
+    self.one()
 
   # --------------------------------------------------------------------