Fixes issues revealed by the new loadsave.py example program.

examples/loadsave.py

@@ -0,0 +1,50 @@
+"""A simple example which loads a SEG Y file and saves it again.
+
+Usage:
+
+    loadsave.py <in.segy> <out.segy>
+
+"""
+import os
+
+import sys
+import traceback
+
+from segpy.reader import create_reader
+from segpy.writer import write_segy
+
+
+def load_save(in_filename, out_filename):
+    with open(in_filename, 'rb') as in_file, \
+         open(out_filename, 'wb') as out_file:
+
+        segy_reader = create_reader(in_file)
+        write_segy(out_file, segy_reader)
+
+
+def main(argv=None):
+    if argv is None:
+        argv = sys.argv[1:]
+
+    try:
+        in_filename = argv[0]
+        out_filename = argv[1]
+    except IndexError:
+        print(globals()['__doc__'], file=sys.stderr)
+        return os.EX_USAGE
+
+    try:
+        load_save(in_filename, out_filename)
+    except (FileNotFoundError, IsADirectoryError) as e:
+        print(e, file=sys.stderr)
+        return os.EX_NOINPUT
+    except PermissionError as e:
+        print(e, file=sys.stderr)
+        return os.EX_NOPERM
+    except Exception as e:
+        traceback.print_exception(type(e), e, e.__traceback__, file=sys.stderr)
+        return os.EX_SOFTWARE
+    return os.EX_OK
+
+if __name__ == '__main__':
+    sys.exit(main())