156             # Convert most string literals to byte literals. String literals

   157             # in Python 2 are bytes. String literals in Python 3 are unicode.

   158             # Most strings in Mercurial are bytes and unicode strings are rare.

   159             # Rather than rewrite all string literals to use ``b''`` to indicate

   160             # byte strings, we apply this token transformer to insert the ``b``

   161             # prefix nearly everywhere.

   162             if t.type == token.STRING:

   163                 s = t.string

   164 

   165                 # Preserve docstrings as string literals. This is inconsistent

   166                 # with regular unprefixed strings. However, the

   167                 # "from __future__" parsing (which allows a module docstring to

   168                 # exist before it) doesn't properly handle the docstring if it

   169                 # is b''' prefixed, leading to a SyntaxError. We leave all

   170                 # docstrings as unprefixed to avoid this. This means Mercurial

   171                 # components touching docstrings need to handle unicode,

   172                 # unfortunately.

   173                 if s[0:3] in ("'''", '"""'):

   174                     yield t

   175                     continue

   176 

   177                 # If the first character isn't a quote, it is likely a string

   178                 # prefixing character (such as 'b', 'u', or 'r'. Ignore.

   179                 if s[0] not in ("'", '"'):

   180                     yield t

   181                     continue

   182 

   183                 # String literal. Prefix to make a b'' string.

   184                 yield t._replace(string='b%s' % t.string)

   185                 continue

   186