Source Code for Module osh.function

  1  # osh 
  2  # Copyright (C) 2005 Jack Orenstein <jao@geophile.com> 
  3  # 
  4  # This program is free software; you can redistribute it and/or modify 
  5  # it under the terms of the GNU General Public License as published by 
  6  # the Free Software Foundation; either version 2 of the License, or 
  7  # (at your option) any later version. 
  8  # 
  9  # This program is distributed in the hope that it will be useful, 
 10  # but WITHOUT ANY WARRANTY; without even the implied warranty of 
 11  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 12  # GNU General Public License for more details. 
 13  # 
 14  # You should have received a copy of the GNU General Public License 
 15  # along with this program; if not, write to the Free Software 
 16  # Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 
 17   
 18  """Encapsulates functions used in osh commands such as C{f} and C{select}. 
 19   
 20  osh function syntax:: 
 21   
 22      [[lambda] ARGS:] EXPRESSION 
 23   
 24  C{ARGS}: Comma-separated list of function arguments, optionally preceded by keyword 
 25  C{lambda}. C{ARGS} may be omitted only for a function with no arguments. 
 26   
 27  C{EXPRESSION}: A Python expression written in terms of the function arguments. 
 28   
 29  Example:: 
 30   
 31      x: max(x, 10) 
 32  """ 
 33   
 34  import copy 
 35  import sys 
 36  import types 
 37   
 38  import core 
 39   
 40  _LAMBDA = 'lambda ' 
 41  _LAMBDA_COLON = 'lambda:' 
 42   
 43  # "Private" name (with leading underscore) so that epydoc doesn't document the class 
 44 -class _Function(object): 
 45      """Represents a function for use by osh commands with function arguments, 
 46      e.g., select. 
 47      """ 
 48       
 49      _function_spec = None 
 50      _function = None 
 51      _function_id = None 
 52   
 53 -    def __init__(self, function_spec, namespace = core.__dict__): 
 54          """Creates a Function. 
 55          - function_spec: String specification of a function. Uses lambda notation, 
 56            but the 'lambda' keyword is optional. 
 57          - namespace: The default is reasonable; there's been no need to 
 58            override it so far. 
 59          """ 
 60          if type(function_spec) in (types.FunctionType, types.BuiltinFunctionType): 
 61              self._function = function_spec 
 62          else: 
 63              self._function_spec = function_spec 
 64              lambda_expression = self.parse(function_spec.strip()) 
 65              # Create a namespace including symbols defined by the current osh invocation. 
 66              namespace = copy.copy(namespace) 
 67              namespace.update(core.namespace()) 
 68              self._function = eval(lambda_expression, namespace) 
 69   
 70 -    def __repr__(self): 
 71          return 'function(%s)' % self._function_spec 
 72               
 73 -    def __call__(self, *args): # args = None): 
 74          return self._function(*args) 
 75   
 76 -    def parse(self, function_spec): 
 77          # If the function spec starts with a lambda, then just use it as is. 
 78          # Otherwise, it could be: 
 79          # - function with arg list, e.g. "x, y: x + y" 
 80          # - zero-arg list with colon, e.g. ": processes()" 
 81          # - zero-arg list without colon, e.g. "processes()" 
 82          # Try prepending "lambda:" and "lambda" until there's 
 83          # no syntax error. Crude but effective. 
 84          if function_spec.startswith(_LAMBDA) or function_spec.startswith(_LAMBDA_COLON): 
 85              # ok as is 
 86              pass 
 87          else: 
 88              fixed_function_spec = '%s: %s' % (_LAMBDA, function_spec) 
 89              try: 
 90                  eval(fixed_function_spec) 
 91                  function_spec = fixed_function_spec 
 92              except: 
 93                  fixed_function_spec = '%s %s' % (_LAMBDA, function_spec) 
 94                  try: 
 95                      eval(fixed_function_spec) 
 96                      function_spec = fixed_function_spec 
 97                  except: 
 98                      raise Exception('Illegal function spec: %s' % function_spec) 
 99          return function_spec 
100