bulletml/expr.py

   1 """BulletML expression evaluator.
   2
   3 http://www.asahi-net.or.jp/~cs8k-cyu/bulletml/index_e.html
   4 """
   5
   6 # BulletML assumes 1/2 = 0.5.
   7 from __future__ import division
   8
   9 import random
  10 import re
  11
  12 from bulletml.errors import Error
  13
  14 __all__ = ["ExprError", "NumberDef", "INumberDef"]
  15
  16 class ExprError(Error):
  17     """Raised when an invalid expression is evaluated/compiled."""
  18     pass
  19
  20 class NumberDef(object):
  21     """BulletML numeric expression.
  22
  23     This translates BulletML numeric expressions into Python expressions.
  24
  25     Examples:
  26     35
  27     360/16
  28     0.7 + 0.9*$rand
  29     180-$rank*20
  30     (2+$1)*0.3
  31
  32     """
  33
  34     GLOBALS = dict(random=random.random, __builtins__={})
  35
  36     def __init__(self, expr):
  37         try:
  38             expr = expr.string
  39         except AttributeError:
  40             pass
  41         try:
  42             if "__" in expr:
  43                 # nedbatchelder.com/blog/201206/eval_really_is_dangerous.html
  44                 raise ExprError(expr)
  45         except TypeError:
  46             pass
  47         self.string = expr = str(expr)
  48         repl = lambda match: "params[%d]" % (int(match.group()[1:]) - 1)
  49         expr = re.sub(r"\$\d+", repl, expr.lower())
  50         self.__expr = expr.replace("$rand", "random()").replace("$rank", "rank")
  51         try:
  52             try:
  53                 self._value = eval(self.__expr, dict(__builtins__={}))
  54             except NameError:
  55                 variables = dict(rank=1, params=[0] * 99)
  56                 value = eval(self.__expr, self.GLOBALS, variables)
  57                 if not isinstance(value, (int, float)):
  58                     raise TypeError(expr)
  59                 self._value = None
  60                 self.expr = self.string
  61             else:
  62                 self.expr = self._value
  63         except Exception:
  64             raise ExprError(expr)
  65         self.__expr = compile(self.__expr, __file__, "eval")
  66
  67     def __call__(self, params, rank):
  68         """Evaluate the expression and return its value."""
  69         if self._value is not None:
  70             return self._value
  71         variables = { 'rank': rank, 'params': params }
  72         return eval(self.__expr, self.GLOBALS, variables)
  73
  74     def __repr__(self):
  75         return "%s(%r)" % (type(self).__name__, self.expr)
  76
  77 class INumberDef(NumberDef):
  78     """A NumberDef, but returns rounded integer results."""
  79     def __init__(self, expr):
  80         super(INumberDef, self).__init__(expr)
  81         if self._value is not None:
  82             self._value = int(round(self._value))
  83
  84     def __call__(self, params, rank):
  85         # Avoid int(round(__call__())) overhead for constants.
  86         if self._value is not None:
  87             return self._value
  88         return int(round(super(INumberDef, self).__call__(params, rank)))