diff --git a/pygmx/__init__.py b/pygmx/__init__.py
index b064c28..aeab992 100644
--- a/pygmx/__init__.py
+++ b/pygmx/__init__.py
@@ -5,3 +5,21 @@ Python wrapper for the gromacs library.
 from .tpxio import TPXReader
 from .xtcio import XTCReader
 # from .enxio import EDRFile
+from .errors import FileTypeError
+from .gromacs.reader import index_filename_for_xtc
+
+FILE_EXTENSIONS = {
+    'xtc': XTCReader,
+    'tpr': TPXReader
+}
+
+
+def open(filename):
+    """Open a supported gromacs file with the appropiate reader."""
+    ext = filename.split('.')[-1]
+    if ext in FILE_EXTENSIONS:
+        if ext in ['xtc']:
+            indexfile = index_filename_for_xtc(filename)
+            return FILE_EXTENSIONS[ext](filename, indexfile)
+    else:
+        raise FileTypeError('Filetype {} not supported by pygmx.'.format(ext))
diff --git a/pygmx/errors.py b/pygmx/errors.py
new file mode 100644
index 0000000..3be2849
--- /dev/null
+++ b/pygmx/errors.py
@@ -0,0 +1,16 @@
+"""Exceptions of the pygmx package."""
+
+
+class InvalidMagicException(Exception): pass
+
+
+class InvalidIndexException(Exception): pass
+
+
+class UnknownLenError(Exception): pass
+
+
+class FileTypeError(Exception): pass
+
+
+class XTCError(Exception): pass
diff --git a/pygmx/xtcio.pyx b/pygmx/xtcio.pyx
index 8bf334b..2960d15 100644
--- a/pygmx/xtcio.pyx
+++ b/pygmx/xtcio.pyx
@@ -11,7 +11,8 @@ import os
 from utility cimport *
 from math cimport *
 from fileio cimport *
-from gromacs.reader import InvalidIndexException, InvalidMagicException, INDEX_MAGIC, SubscriptableReader, XTCFrame
+from .gromacs.reader import INDEX_MAGIC, SubscriptableReader, XTCFrame
+from .errors import InvalidIndexException, InvalidMagicException, XTCError
 
 
 cdef extern from "gromacs/fileio/xtcio.h":
@@ -67,9 +68,6 @@ cdef array get_xtc_index(t_fileio *fio):
     return cache[:-1]
 
 
-class XTCError(Exception): pass
-
-
 cdef class XTCReader:
     cdef:
         t_fileio *fio