Fix binding of UTF8Alphabet class in decoder package

Author: reuben

native_client/ctcdecode/__init__.py

@@ -1,7 +1,6 @@
 from __future__ import absolute_import, division, print_function
 
 from . import swigwrapper # pylint: disable=import-self
-from .swigwrapper import UTF8Alphabet
 
 # This module is built with SWIG_PYTHON_STRICT_BYTE_CHAR so we must handle
 # string encoding explicitly, here and throughout this file.
@@ -89,6 +88,56 @@ def Decode(self, input):
         return res.decode('utf-8')
 
 
+class UTF8Alphabet(swigwrapper.UTF8Alphabet):
+    """Convenience wrapper for Alphabet which calls init in the constructor"""
+    def __init__(self):
+        super(UTF8Alphabet, self).__init__()
+        err = self.init(b'')
+        if err != 0:
+            raise ValueError('UTF8Alphabet initialization failed with error code 0x{:X}'.format(err))
+
+    def CanEncodeSingle(self, input):
+        '''
+        Returns true if the single character/output class has a corresponding label
+        in the alphabet.
+        '''
+        return super(UTF8Alphabet, self).CanEncodeSingle(input.encode('utf-8'))
+
+    def CanEncode(self, input):
+        '''
+        Returns true if the entire string can be encoded into labels in this
+        alphabet.
+        '''
+        return super(UTF8Alphabet, self).CanEncode(input.encode('utf-8'))
+
+    def EncodeSingle(self, input):
+        '''
+        Encode a single character/output class into a label. Character must be in
+        the alphabet, this method will assert that. Use `CanEncodeSingle` to test.
+        '''
+        return super(UTF8Alphabet, self).EncodeSingle(input.encode('utf-8'))
+
+    def Encode(self, input):
+        '''
+        Encode a sequence of character/output classes into a sequence of labels.
+        Characters are assumed to always take a single Unicode codepoint.
+        Characters must be in the alphabet, this method will assert that. Use
+        `CanEncode` and `CanEncodeSingle` to test.
+        '''
+        # Convert SWIG's UnsignedIntVec to a Python list
+        res = super(UTF8Alphabet, self).Encode(input.encode('utf-8'))
+        return [el for el in res]
+
+    def DecodeSingle(self, input):
+        res = super(UTF8Alphabet, self).DecodeSingle(input)
+        return res.decode('utf-8')
+
+    def Decode(self, input):
+        '''Decode a sequence of labels into a string.'''
+        res = super(UTF8Alphabet, self).Decode(input)
+        return res.decode('utf-8')
+
+
 
 def ctc_beam_search_decoder(probs_seq,
                             alphabet,