xorn/src/gaf/netlist/backend.py

   1 # gaf.netlist - gEDA Netlist Extraction and Generation
   2 # Copyright (C) 1998-2010 Ales Hvezda
   3 # Copyright (C) 1998-2010 gEDA Contributors (see ChangeLog for details)
   4 # Copyright (C) 2013-2020 Roland Lutz
   5 #
   6 # This program is free software; you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation; either version 2 of the License, or
   9 # (at your option) any later version.
  10 #
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 # GNU General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program; if not, write to the Free Software Foundation,
  18 # Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  19
  20 ## \namespace gaf.netlist.backend
  21 ## Handling netlist backends.
  22 #
  23 # After the netlist has been constructed, it is passed to a \a backend
  24 # which creates some kind of output based on the information in the
  25 # netlist.  The backend is selected by the user via the command-line
  26 # option <tt>-g \a BACKEND</tt>; a list of available options can be
  27 # displayed using the command-line option `--list-backends`.
  28 #
  29 # A backend is a Python file in the special backend load path whose
  30 # name starts with the prefix \c "gnet_".  It should contain a special
  31 # function \c run(f, netlist) as the main entry point.
  32
  33 import imp, os, sys
  34 from gettext import gettext as _
  35
  36 ## Module name prefix for netlister backends.
  37 #
  38 # Only Python modules whose name starts with this prefix are
  39 # considered netlister backends.
  40
  41 BACKEND_PREFIX = 'gnet_'
  42
  43 ## Backend load path.
  44 #
  45 # A list of directory names in which to search for netlister backends.
  46
  47 load_path = []
  48
  49 ## Get a sorted list of available backends.
  50 #
  51 # Returns a list of available netlister backends by searching for
  52 # files in each of the directories given in \ref load_path.  A module
  53 # is considered to be a netlister backend if its name begins with
  54 # \ref BACKEND_PREFIX ("gnet_").
  55
  56 def list_backends():
  57     backend_names = set()
  58
  59     for dir_name in load_path:
  60         try:
  61             d_names = os.listdir(dir_name)
  62         except OSError as e:
  63             sys.stderr.write(_("Can't open directory %s: %s\n")
  64                              % (dir_name, e.strerror))
  65             continue
  66
  67         for d_name in d_names:
  68             # Check that filename has the right format to be a backend
  69             if not d_name.startswith(BACKEND_PREFIX):
  70                 continue
  71
  72             for suffix, mode, type in imp.get_suffixes():
  73                 if d_name.endswith(suffix, len(BACKEND_PREFIX)):
  74                     # Remove prefix & suffix.  Add to list of backend names.
  75                     backend_names.add(d_name[len(BACKEND_PREFIX):-len(suffix)])
  76                     break
  77
  78     return sorted(backend_names)
  79
  80 ## Load a specific netlister backend.
  81 #
  82 # Searches in the backend load path for a module called \c
  83 # gnet_<em>backend_name</em>, loads it, and returns the module object.
  84 #
  85 # The backend module's path is added to the system load path.
  86 #
  87 # \throws ImportError if the module could not be loaded
  88
  89 def load(backend_name):
  90     # Search for backend module in load path
  91     f, pathname, description = imp.find_module(
  92         BACKEND_PREFIX + backend_name, load_path)
  93     if f is None:
  94         # module is a package
  95         raise ImportError
  96
  97     # Load backend code.
  98     sys.path.insert(0, os.path.dirname(pathname))
  99     try:
 100         return imp.load_module(BACKEND_PREFIX + backend_name,
 101                                f, pathname, description)
 102     finally:
 103         f.close()