AppPkg/Applications/Python/Python-2.7.2/Lib/lib2to3/fixes/fix_raise.py

   1 """Fixer for 'raise E, V, T'
   2
   3 raise         -> raise
   4 raise E       -> raise E
   5 raise E, V    -> raise E(V)
   6 raise E, V, T -> raise E(V).with_traceback(T)
   7 raise E, None, T -> raise E.with_traceback(T)
   8
   9 raise (((E, E'), E''), E'''), V -> raise E(V)
  10 raise "foo", V, T               -> warns about string exceptions
  11
  12
  13 CAVEATS:
  14 1) "raise E, V" will be incorrectly translated if V is an exception
  15    instance. The correct Python 3 idiom is
  16
  17         raise E from V
  18
  19    but since we can't detect instance-hood by syntax alone and since
  20    any client code would have to be changed as well, we don't automate
  21    this.
  22 """
  23 # Author: Collin Winter
  24
  25 # Local imports
  26 from .. import pytree
  27 from ..pgen2 import token
  28 from .. import fixer_base
  29 from ..fixer_util import Name, Call, Attr, ArgList, is_tuple
  30
  31 class FixRaise(fixer_base.BaseFix):
  32
  33     BM_compatible = True
  34     PATTERN = """
  35     raise_stmt< 'raise' exc=any [',' val=any [',' tb=any]] >
  36     """
  37
  38     def transform(self, node, results):
  39         syms = self.syms
  40
  41         exc = results["exc"].clone()
  42         if exc.type == token.STRING:
  43             msg = "Python 3 does not support string exceptions"
  44             self.cannot_convert(node, msg)
  45             return
  46
  47         # Python 2 supports
  48         #  raise ((((E1, E2), E3), E4), E5), V
  49         # as a synonym for
  50         #  raise E1, V
  51         # Since Python 3 will not support this, we recurse down any tuple
  52         # literals, always taking the first element.
  53         if is_tuple(exc):
  54             while is_tuple(exc):
  55                 # exc.children[1:-1] is the unparenthesized tuple
  56                 # exc.children[1].children[0] is the first element of the tuple
  57                 exc = exc.children[1].children[0].clone()
  58             exc.prefix = u" "
  59
  60         if "val" not in results:
  61             # One-argument raise
  62             new = pytree.Node(syms.raise_stmt, [Name(u"raise"), exc])
  63             new.prefix = node.prefix
  64             return new
  65
  66         val = results["val"].clone()
  67         if is_tuple(val):
  68             args = [c.clone() for c in val.children[1:-1]]
  69         else:
  70             val.prefix = u""
  71             args = [val]
  72
  73         if "tb" in results:
  74             tb = results["tb"].clone()
  75             tb.prefix = u""
  76
  77             e = exc
  78             # If there's a traceback and None is passed as the value, then don't
  79             # add a call, since the user probably just wants to add a
  80             # traceback. See issue #9661.
  81             if val.type != token.NAME or val.value != u"None":
  82                 e = Call(exc, args)
  83             with_tb = Attr(e, Name(u'with_traceback')) + [ArgList([tb])]
  84             new = pytree.Node(syms.simple_stmt, [Name(u"raise")] + with_tb)
  85             new.prefix = node.prefix
  86             return new
  87         else:
  88             return pytree.Node(syms.raise_stmt,
  89                                [Name(u"raise"), Call(exc, args)],
  90                                prefix=node.prefix)