diff --git a/swiftsimio/masks.py b/swiftsimio/masks.py
index b3f406ca..9564f5ae 100644
--- a/swiftsimio/masks.py
+++ b/swiftsimio/masks.py
@@ -10,7 +10,7 @@
 
 import numpy as np
 
-from swiftsimio import SWIFTMetadata
+from swiftsimio.metadata.objects import SWIFTMetadata
 
 from swiftsimio.objects import InvalidSnapshot
 
@@ -423,9 +423,6 @@ def constrain_index(self, index: int):
         index : int
             The index of the row to select.
         """
-        if not self.metadata.filetype == "SOAP":
-            warnings.warn("Not masking a SOAP catalogue, nothing constrained.")
-            return
         for group_name in self.metadata.present_group_names:
             setattr(self, group_name, np.array([[index, index + 1]]))
             setattr(self, f"{group_name}_size", 1)
diff --git a/swiftsimio/reader.py b/swiftsimio/reader.py
index 809b3817..f2e6ec61 100644
--- a/swiftsimio/reader.py
+++ b/swiftsimio/reader.py
@@ -11,27 +11,20 @@
 + SWIFTDataset, a container class for all of the above.
 """
 
-
 from swiftsimio.accelerated import read_ranges_from_file
-from swiftsimio.objects import cosmo_array, cosmo_factor, a
+from swiftsimio.objects import cosmo_array, cosmo_factor
 
 from swiftsimio.metadata.objects import (
     metadata_discriminator,
     SWIFTUnits,
     SWIFTGroupMetadata,
-    SWIFTMetadata,
 )
 
-import re
 import h5py
 import unyt
 import numpy as np
-import warnings
-
-from datetime import datetime
-from pathlib import Path
 
-from typing import Union, Callable, List, Optional
+from typing import Union, List
 
 
 def generate_getter(
@@ -181,9 +174,11 @@ def getter(self):
                             cosmo_array(
                                 # Only use column data if array is multidimensional, otherwise
                                 # we will crash here
-                                handle[field][:, columns]
-                                if handle[field].ndim > 1
-                                else handle[field][:],
+                                (
+                                    handle[field][:, columns]
+                                    if handle[field].ndim > 1
+                                    else handle[field][:]
+                                ),
                                 unit,
                                 cosmo_factor=cosmo_factor,
                                 name=description,
@@ -316,7 +311,7 @@ def generate_empty_properties(self):
 class __SWIFTNamedColumnDataset(object):
     """
     Holder class for individual named datasets. Very similar to
-    __SWIFTGroupsDatasets but much simpler.
+    __SWIFTGroupDatasets but much simpler.
     """
 
     def __init__(self, field_path: str, named_columns: List[str], name: str):
diff --git a/swiftsimio/subset_writer.py b/swiftsimio/subset_writer.py
index 235cbbe2..da7b03f3 100644
--- a/swiftsimio/subset_writer.py
+++ b/swiftsimio/subset_writer.py
@@ -3,12 +3,10 @@
 it to a new file.
 """
 
-from swiftsimio.reader import SWIFTUnits, SWIFTMetadata
 from swiftsimio.masks import SWIFTMask
 from swiftsimio.accelerated import read_ranges_from_file
 import swiftsimio.metadata as metadata
 
-import unyt
 import h5py
 import numpy as np
 from typing import Optional, List