Factor byte-to-string conversion out into byte_string

No need to repeat this code everywhere we want to stringify some
bytes.

diff --git a/gpg-migrate.py b/gpg-migrate.py
index 8d475f76e86f75436dde8c69221adbbed6e82942..e376f8d5bf3bccc2086699f185d8ce6a39759163 100755 (executable)
--- a/gpg-migrate.py
+++ b/gpg-migrate.py
@@ -25,6 +25,26 @@ def _get_stdout(args, stdin=None):
     return stdout
 
 
+def byte_string(data, sep=' '):
+    r"""Convert a byte-string to human readable form
+
+    >>> byte_string(b'\x12\x34\x56')
+    '12 34 56'
+    """
+    return sep.join('{:02x}'.format(byte) for byte in data)
+
+
+def string_bytes(data, sep=' '):
+    r"""Reverse byte_string()
+
+    >>> string_bytes('12 fa fb')
+    b'\x12\xfa\xfb'
+    """
+    return bytes(
+        int(c1+c2, base=16) for c1,c2 in
+        zip(data[::2 + len(sep)], data[1::2 + len(sep)]))
+
+
 class PGPPacket (dict):
     # http://tools.ietf.org/search/rfc4880
     _old_format_packet_length_type = {  # type: (bytes, struct type)
@@ -325,7 +345,7 @@ class PGPPacket (dict):
             if key in self:
                 value = self[key]
                 if isinstance(value, bytes):
-                    value = ' '.join('{:02x}'.format(byte) for byte in value)
+                    value = byte_string(data=value)
                 lines.append('  {}: {}'.format(label, value))
         return '\n'.join(lines)
 
@@ -711,7 +731,7 @@ class PGPPacket (dict):
         subpacket['signature-creation-time'] = _struct.unpack('>I', data)[0]
 
     def _parse_issuer_signature_subpacket(self, data, subpacket):
-        subpacket['issuer'] = ''.join('{:02x}'.format(byte) for byte in data)
+        subpacket['issuer'] = byte_string(data=data, sep='')
 
     def _parse_key_expiration_time_signature_subpacket(
             self, data, subpacket):
@@ -996,9 +1016,8 @@ class PGPPacket (dict):
                     raise ValueError(
                         ('serialized {} differs from input packet: '
                          'at byte {}, {} != {}').format(
-                            self['type'], i,
-                            ' '.join('{:02x}'.format(byte) for byte in out_chunk),
-                            ' '.join('{:02x}'.format(byte) for byte in in_chunk)))
+                            self['type'], i, byte_string(data=out_chunk),
+                            byte_string(data=in_chunk)))
 
 
 class PGPKey (object):