pyx/attr.py

   1 #!/usr/bin/env python
   2 # -*- coding: ISO-8859-1 -*-
   3 #
   4 #
   5 # Copyright (C) 2003 Jörg Lehmann <joergl@users.sourceforge.net>
   6 # Copyright (C) 2003 Michael Schindler <m-schindler@users.sourceforge.net>
   7 # Copyright (C) 2003 André Wobst <wobsta@users.sourceforge.net>
   8 #
   9 # This file is part of PyX (http://pyx.sourceforge.net/).
  10 #
  11 # PyX is free software; you can redistribute it and/or modify
  12 # it under the terms of the GNU General Public License as published by
  13 # the Free Software Foundation; either version 2 of the License, or
  14 # (at your option) any later version.
  15 #
  16 # PyX is distributed in the hope that it will be useful,
  17 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 # GNU General Public License for more details.
  20 #
  21 # You should have received a copy of the GNU General Public License
  22 # along with PyX; if not, write to the Free Software
  23 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  24
  25
  26 #
  27 # some helper functions for the attribute handling
  28 #
  29
  30 def mergeattrs(attrs):
  31     """perform merging of the attribute list attrs as defined by the
  32     merge methods of the attributes"""
  33     newattrs = []
  34     for attr in attrs:
  35         newattrs = attr.merge(newattrs)
  36     return newattrs
  37
  38
  39 def getattrs(attrs, getclasses):
  40     """return all attributes in the attribute list attrs, which are
  41     instances of one of the classes in getclasses"""
  42     result = []
  43     try:
  44         for attr in attrs:
  45             if isinstance(attr, getclasses):
  46                 result.append(attr)
  47                 break
  48     except TypeError: # workaround for Python 2.1 and older
  49         for attr in attrs:
  50             for getclass in getclasses:
  51                 if isinstance(attr, getclass):
  52                     result.append(attr)
  53                     break
  54     return result
  55
  56
  57 def checkattrs(attrs, allowedclasses):
  58     """check whether only attributes which are instances of classes in
  59     allowedclasses are present in the attribute list attrs"""
  60     if len(attrs) != len(getattrs(attrs, allowedclasses)):
  61         for attr1, attr2 in zip(attrs, getattrs(attrs, allowedclasses)):
  62             if attr1 is not attr2:
  63                 raise TypeError("instance %r not allowed" % attr1)
  64         else:
  65             raise TypeError("instance %r not allowed" % attrs[len(getattrs(attrs, allowedclasses))])
  66
  67 #
  68 # attr class and simple descendants
  69 #
  70
  71 class attr:
  72
  73     """ attr is the base class of all attributes, i.e., colors, decorators,
  74     styles, text attributes and trafos"""
  75
  76     def merge(self, attrs):
  77         """merge self into list of attrs
  78
  79         self may either be appended to attrs or inserted at a proper position
  80         immediately before a dependent attribute. Attributes of the same type
  81         should be removed, if redundant. Note that it is safe to modify
  82         attrs."""
  83
  84         attrs.append(self)
  85         return attrs
  86
  87
  88 class exclusiveattr(attr):
  89
  90     """an attribute which swallows all but the last of the same type in an
  91     attribute list"""
  92
  93     def __init__(self, exclusiveclass):
  94         self.exclusiveclass = exclusiveclass
  95
  96     def merge(self, attrs):
  97         attrs = [attr for attr in attrs if not isinstance(attr, self.exclusiveclass)]
  98         attrs.append(self)
  99         return attrs
 100
 101
 102 class clearclass(attr):
 103
 104     """a special attribute which allows to remove all predecessing attributes of
 105     the same type in an attribute list"""
 106
 107     def __init__(self, clearclass):
 108         self.clearclass = clearclass
 109
 110     def merge(self, attrs):
 111         return [attr for attr in attrs if not isinstance(attr, self.clearclass)]
 112
 113
 114 # XXX is _clear a good choice?
 115
 116 class _clear(attr):
 117
 118     """a special attribute which removes all predecessing attributes
 119     in an attribute list"""
 120
 121     def merge(self, attrs):
 122         return []
 123
 124 # we define the attribute "clear", an instance of "_clear",
 125 # which can be used to remove all predecessing attributes
 126 # in an attribute list
 127
 128 clear = _clear()
 129