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 class ExprError(Error):
  15     """Raised when an invalid expression is evaluated/compiled."""
  16     pass
  17
  18 class NumberDef(object):
  19     """BulletML numeric expression.
  20
  21     This translates BulletML numeric expressions into Python expressions.
  22     The
  23
  24     Examples:
  25     35
  26     360/16
  27     0.7 + 0.9*$rand
  28     180-$rank*20
  29     (2+$1)*0.3
  30
  31     """
  32
  33     GLOBALS = dict(random=random.random, __builtins__={})
  34     def __init__(self, expr):
  35         try:
  36             expr = expr.__original
  37         except AttributeError:
  38             pass
  39         self.__original = expr
  40         repl = lambda match: "params[%d]" % (int(match.group()[1:]) - 1)
  41         expr = re.sub(r"\$\d+", repl, expr.lower())
  42         self.__expr = expr.replace("$rand", "random()").replace("$rank", "rank")
  43         try:
  44             try:
  45                 self.__value = eval(self.__expr, dict(__builtins__={}))
  46             except NameError:
  47                 variables = dict(rank=1, params=[0] * 99)
  48                 value = eval(self.__expr, self.GLOBALS, variables)
  49                 if not isinstance(value, (int, float)):
  50                     raise TypeError(expr)
  51                 self.__value = None
  52         except Exception:
  53             raise ExprError(expr)
  54         self.__expr = compile(self.__expr, __file__, "eval")
  55
  56     def __call__(self, params, rank):
  57         """Evaluate the expression and return its value."""
  58         if self.__value is not None:
  59             return self.__value
  60         variables = { 'rank': rank, 'params': params }
  61         return eval(self.__expr, self.GLOBALS, variables)
  62
  63     def __repr__(self):
  64         return "%s(%r)" % (type(self).__name__, self.__original)
  65
  66 class INumberDef(NumberDef):
  67     """A NumberDef, but returns rounded integer results."""
  68     def __call__(self, params, rank):
  69         return int(round(super(INumberDef, self).__call__(params, rank)))