Returns:
A list of lines from the read and transformed file contents.
+
+ Raises:
+ Exception: filename not found or can't be read.
"""
ret = []
on_error: If set, it's invoked on error conditions and passed then
path and OSError that it caused.
+ Raises:
+ OSError: an exception occurred and on_error not set.
+
See also :meth:`does_file_exist`.
.. warning::