Determine if an existing file is gzipped based on magic bytes, not suffix

masque/file/gdsii.py

@@ -35,6 +35,7 @@ import gdsii.structure
 import gdsii.elements
 
 from .utils import mangle_name, make_dose_table, dose2dtype, dtype2dose, clean_pattern_vertices
+from .utils import is_gzipped
 from .. import Pattern, SubPattern, PatternError, Label, Shape
 from ..shapes import Polygon, Path
 from ..repetition import Grid
@@ -190,7 +191,7 @@ def readfile(filename: Union[str, pathlib.Path],
     """
     Wrapper for `masque.file.gdsii.read()` that takes a filename or path instead of a stream.
 
-    Will automatically decompress files with a .gz suffix.
+    Will automatically decompress gzipped files.
 
     Args:
         filename: Filename to save to.
@@ -198,7 +199,7 @@ def readfile(filename: Union[str, pathlib.Path],
         **kwargs: passed to `masque.file.gdsii.read`
     """
     path = pathlib.Path(filename)
-    if path.suffix == '.gz':
+    if is_gzipped(path):
         open_func: Callable = gzip.open
     else:
         open_func = open