Clarify documentation for non-numbered input files

screen19/__init__.py

@@ -95,7 +95,7 @@ def prettyprint_procrunner(d):
     )
 
 
-def make_template(f):
+def make_template(f):  # type: (str) -> (str, int)
     """
     Generate a xia2-style filename template.
 
@@ -104,17 +104,22 @@ def make_template(f):
     before the file extension.
     For example, the filename example_01_0001.cbf becomes example_01_####.cbf.
 
+    If the input data are in a single file and its name doesn't match the above
+    template, the resulting filename template is simply the input file name and the
+    resultant image number is None.
+    This might be the case for input data in NeXus NXmx HDF5 format, for example,
+    where one typically passes a file with a name like example_master.h5.
+
     :param f: Filename, with extension.
-    :type f: str
     :return: Filename template, with extension; image number.
-    :rtype: Tuple(str, int)
     """
     # Split the file from its path
     directory, f = os.path.split(f)
     # Split off the file extension, assuming it begins at the first full stop,
     # also split the last contiguous group of digits off the filename root
     try:
         root, number, extension = re.split(r"([0-9#]+)(?=\.\w)", f, 1)
+    # Catch the case where the input data file name doesn't match the numbered pattern.
     except ValueError:
         template = f
         image = None