pyvconv.py

   1 import libxml2
   2 import re
   3
   4 class Error(Exception):
   5     def __init__(self, value):
   6         Exception.__init__(self)
   7         self.value = value
   8     def __str__(self):
   9         return repr(self.value)
  10
  11 class Variable:
  12     def __init__(self, namestr, defaultstr, exprstr):
  13         self.namestr = namestr
  14         self.defaultstr = defaultstr
  15         self.exprstr = exprstr
  16
  17     def __str__(self):
  18         return self.namestr
  19
  20     def has_value(self):
  21         return self.defaultstr != None
  22
  23     def evaluate(self):
  24         if self.defaultstr == None:
  25             raise Error("Error: Trying to eval variable " + self.namestr + " with no value")
  26         return self.defaultstr
  27
  28 class OptionalSetting:
  29     def __init__(self, namestr, exprstr):
  30         self.namestr = namestr
  31         self.exprstr = exprstr
  32
  33     def get_name(self):
  34         return self.namestr
  35
  36     def evaluate(self, var_list):
  37         instr = self.exprstr
  38         for var in var_list:
  39             if var_list[var].has_value():
  40                 p = re.compile( "\$\{" + var + "\}")
  41                 instr = p.sub( var_list[var].evaluate(), instr)
  42         if instr.find("$") != -1:
  43             instr = "" # if not all variables were found, return empty option
  44         return instr
  45
  46 class RenderCommand:
  47     def __init__(self, namestr, callstr, var_list, optset_list):
  48         self.namestr = namestr
  49         self.callstr = callstr
  50         self.var_list = var_list
  51         self.optset_list = optset_list
  52
  53     def get_name(self):
  54         return self.namestr
  55
  56     def put_var(self, var):
  57         self.var_list[str(var)] = var
  58
  59     def get_vars(self):
  60         return self.var_list
  61
  62     def evaluate(self):
  63         instr = self.callstr
  64
  65         p = re.compile("\$\[(\w+)\]")
  66         for o in p.findall(instr):
  67             if o not in self.optset_list:
  68                 raise Error("Error: Optional variable not defined")
  69             instr = p.sub(self.optset_list[o].evaluate(self.var_list), instr)
  70
  71         p = re.compile("\$\{(\w+)\}")
  72         for o in p.findall(instr):
  73             if o not in self.var_list:
  74                 raise Error("Error: Variable \"" + o + "\" has not been assigned")
  75             val = self.var_list[o].evaluate()
  76             instr = instr.replace("${" + o + "}", val)
  77
  78         if instr.find("$") != -1:
  79             raise Error("Error: all variables were not expanded")
  80         return instr
  81
  82     def __str__(self):
  83         return self.evaluate()
  84
  85 class RenderCommands:
  86     def __init__(self):
  87         self.cmdcall_dict = {}
  88         self._read_config()
  89
  90     def _read_properties(self, propnode, mand_propnames, opt_propnames = []):
  91         propdict = {}
  92
  93         for p in propnode:
  94             if p.name in mand_propnames:
  95                 propdict[p.name] = str(p.content)
  96             elif p.name != "text" and p.name not in opt_propnames:
  97                 raise Error("Error parsing XML: only name and call are accepted properties in the element command, found " + str(p.name))
  98
  99         if len(mand_propnames) != len(propdict.keys()):
 100             raise Error("Error parsing XML: must supply both name and call in element command")
 101
 102         for p in propnode:
 103             if p.name in opt_propnames:
 104                 propdict[p.name] = str(p.content)
 105             elif p.name != "text" and p.name not in mand_propnames:
 106                 raise Error("Error parsing XML: only name and call are accepted properties in the element command, found " + str(p.name))
 107
 108         return propdict
 109
 110     def _read_config(self):
 111         doc = libxml2.parseFile("rendercommands.xml")
 112         cmd_xmllist = doc.xpathEval( '//command')
 113
 114         # read all commands from XML description
 115         for cmdnode in cmd_xmllist:
 116             if cmdnode.type == "element" and cmdnode.name == "command":
 117
 118                 var_list = {}
 119                 optset_list = {}
 120
 121                 if cmdnode.children:
 122                     for varsetnode in cmdnode.children:
 123                         if varsetnode.type == "element" and varsetnode.name == "variable":
 124                             props =  self._read_properties(varsetnode.properties, ["name", "expr"], ["default"])
 125                             defprop = None
 126                             if "default" in props:
 127                                 defprop = props["default"]
 128                             var_list[props["name"]] = Variable(props["name"], defprop, props["expr"])
 129
 130                         elif varsetnode.type == "element" and varsetnode.name == "optionalsetting":
 131                             props = self._read_properties(varsetnode.properties, ["name", "expr"])
 132                             optset_list[props["name"]] = OptionalSetting(props["name"], props["expr"])
 133
 134                         elif varsetnode.name != "text":
 135                             raise Error("Error parsing XML: only variable and optionalsetting elements allowed in command")
 136
 137                 props = self._read_properties(cmdnode.properties, ["name", "call"])
 138                 self.cmdcall_dict[props["name"]] = RenderCommand(props["name"], props["call"], var_list, optset_list)
 139
 140             else:
 141                 raise Error("Error parsing XML: only command elements are supported")
 142
 143     def __iter__(self):
 144         return self.cmdcall_dict.values().__iter__()
 145
 146 def main():
 147     commands = RenderCommands()
 148     for c in commands:
 149         c.put_var(Variable("in", "src.avi", None))
 150         c.put_var(Variable("out", "dest.avi", None))
 151         print c
 152
 153 if __name__ == "__main__":
 154     main()
 155