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+$1)*0.3
  30
  31     """
  32     def __init__(self, expr):
  33         try:
  34             expr = expr.__original
  35         except AttributeError:
  36             pass
  37         self.__original = expr
  38         repl = lambda match: "params[%d]" % (int(match.group()[1:]) - 1)
  39         expr = re.sub(r"\$\d+", repl, expr.lower())
  40         self.__expr = expr.replace("$rand", "rand").replace("$rank", "rank")
  41         try:
  42             try:
  43                 self.__value = eval(self.__expr, dict(__builtins__={}))
  44             except NameError:
  45                 fake = [0] * 99
  46                 variables = dict(rand=1, rank=1, params=fake, __builtins__={})
  47                 value = eval(self.__expr, variables)
  48                 if not isinstance(value, (int, float)):
  49                     raise TypeError(expr)
  50                 self.__value = None
  51         except Exception:
  52             raise ExprError(expr)
  53         self.__expr = compile(self.__expr, __file__, "eval")
  54
  55     def __call__(self, params, rank):
  56         """Evaluate the expression and return its value."""
  57         if self.__value is not None:
  58             return self.__value
  59         rand = random.random()
  60         variables = dict(rand=rand, rank=rank, params=params)
  61         return eval(self.__expr, variables)
  62
  63     def __repr__(self):
  64         return "%s(%r)" % (type(self).__name__, self.__original)