diff --git a/py/desisurvey/svstats.py b/py/desisurvey/svstats.py
new file mode 100644
index 0000000..0c6d49b
--- /dev/null
+++ b/py/desisurvey/svstats.py
@@ -0,0 +1,55 @@
+import numpy as np
+import desisurvey.tiles
+
+
+def donefrac_in_conditions(condnexp, configfn=None):
+    """Get donefrac corresponding to number of tiles observed
+    in different conditions.
+
+    condnexp from desisurvey.scripts.collect_etc.nexp_in_conditions
+    """
+    import desisurvey.config
+    config = desisurvey.config.Configuration(configfn)
+    tiles = desisurvey.tiles.get_tiles()
+    out = np.zeros(tiles.ntiles, dtype=[
+        ('TILEID', 'i4'),
+        ('DONEFRAC_DARK', 'f4'), ('DONEFRAC_GRAY', 'f4'),
+        ('DONEFRAC_BRIGHT', 'f4'),
+        ('NNIGHT_DARK', 'i4'), ('NNIGHT_GRAY', 'i4'),
+        ('NNIGHT_BRIGHT', 'i4'),
+        ('NNIGHT_NEEDED_DARK', 'i4'), ('NNIGHT_NEEDED_GRAY', 'i4'),
+        ('NNIGHT_NEEDED_BRIGHT', 'i4'),
+    ])
+    if ((len(np.unique(condnexp['TILEID'])) != len(condnexp)) or
+            (len(np.unique(tiles.tileID)) != tiles.ntiles)):
+        raise ValueError('Must be at least one tile per record!')
+    _, mc, mt = np.intersect1d(condnexp['TILEID'], tiles.tileID,
+                               return_indices=True)
+    CONDITIONS = ['DARK', 'GRAY', 'BRIGHT']
+    out['TILEID'] = tiles.tileID
+    for i, program in enumerate(tiles.tileprogram):
+        for cond in CONDITIONS:
+            needed = getattr(getattr(config.completeness, program), cond, None)
+            needed = 0 if needed is None else needed()
+            out['NNIGHT_NEEDED_'+cond][i] = needed
+    for ic, it in zip(mc, mt):
+        for cond in CONDITIONS:
+            nexp = condnexp['NNIGHT_'+cond][ic]
+            program = tiles.tileprogram[it]
+            out['NNIGHT_'+cond][it] = nexp
+    for cond in CONDITIONS:
+        out['DONEFRAC_'+cond] = out['NNIGHT_'+cond]/(
+            out['NNIGHT_NEEDED_'+cond] + (out['NNIGHT_NEEDED_'+cond] == 0))
+    return out
+
+    # we then output for each tile what conditions it's still allowed in,
+    # and whether it's done (allowed_in_conditions = 0).
+
+    # would be straightforward to incorporate completeness information
+    # into optimize.py with an additional ~donefrac data structure
+    # that modifies dlst_nom, multiplying it by (1-donefrac) for each tile
+
+    # that also needs to know the donefrac in each condition.
+    # but first step is just to get the donefracs at all.
+
+    # Build the list of nexp for each of these conditions.