diff --git a/scripts/sample-each-dataset.sh b/scripts/sample-each-dataset.sh
index ca4fa5a..16d0f50 100755
--- a/scripts/sample-each-dataset.sh
+++ b/scripts/sample-each-dataset.sh
@@ -58,25 +58,7 @@ python -m virtualenv $PYVENV
 # ex: /data/sim/IceCube/2023/generated/neutrino-generator/22645 -> depth=0
 # ex: /data/sim/IceCube/2023/generated/neutrino-generator/ -> depth=1
 # ex: /data/sim/IceCube/2023/generated/ -> depth=2
-depth_to_datasets=$(python3 -c "
-from pathlib import Path
-import sys
-
-path = Path(sys.argv[1])
-SIM = 'sim'
-N_SEGMENTS_BASE_TO_DATASET = 5
-
-try:
-    base_index = list(path.parts).index(SIM)
-except ValueError:
-    raise ValueError(f'Path {path} does not contain the base identifier {SIM}/')
-segments_after_base = path.parts[base_index + 1:]
-
-depth = N_SEGMENTS_BASE_TO_DATASET - len(segments_after_base)
-if depth < 0:
-    raise ValueError(f'Path {path} is too specific; the user can supply up to a dataset dir')
-print(depth)
-" "$BASE_PATH" 2>&1)
+depth_to_datasets=$(python -m simprod_histogram.calc_depth_to_dataset_dirs "$BASE_PATH" 2>&1)
 
 #######################################################################################
 # Run!
diff --git a/simprod_histogram/calc_depth_to_dataset_dirs.py b/simprod_histogram/calc_depth_to_dataset_dirs.py
new file mode 100644
index 0000000..c5ee3b4
--- /dev/null
+++ b/simprod_histogram/calc_depth_to_dataset_dirs.py
@@ -0,0 +1,49 @@
+"""Calculate the filetree depth from dirpath to the dataset directories.
+
+See calculate() below for more info.
+"""
+
+import sys
+from pathlib import Path
+
+
+def calculate(dirpath: str) -> int:
+    """
+    Calculate the filetree depth from dirpath to the dataset directories.
+
+    Assumes the naming convention:
+        .../sim/IceCube/<year>/<generated>/<neutrino-generator>/<dataset_id>
+
+    Examples:
+        .../sim/IceCube/2023/generated/neutrino-generator/22645   -> depth=0
+        .../sim/IceCube/2023/generated/neutrino-generator/        -> depth=1
+        .../sim/IceCube/2023/generated/                           -> depth=2
+
+    Note:
+        This does not enforce that the dirpath be rooted at /data/sim, so it
+        allows, both:
+            1. using 'realpath' (ex: /data/sim/IceCube/... -> /mnt/lfs6/sim/IceCube/...)
+            2: running in a testbed directory (ex: /home/eevans/test/data/sim/IceCube/...)
+    """
+    dirpath = Path(dirpath)
+
+    SIM = "sim"  # as in '/data/sim' (or a local tree '/home/.../sim/...')
+    N_SEGMENTS_BASE_TO_DATASET = 5
+
+    try:
+        base_index = list(dirpath.parts).index(SIM)
+    except ValueError:
+        raise ValueError(f"Path {dirpath} does not contain the base identifier {SIM}/")
+    segments_after_base = dirpath.parts[base_index + 1 :]
+
+    depth = N_SEGMENTS_BASE_TO_DATASET - len(segments_after_base)
+    if depth < 0:
+        raise ValueError(
+            f"Path {dirpath} is too specific; the user can supply up to a dataset dir"
+        )
+
+    return depth
+
+
+if __name__ == "__main__":
+    calculate(sys.argv[1])