| paul@6 | 1 | #!/usr/bin/env python |
| paul@6 | 2 | |
| paul@6 | 3 | """ |
| paul@6 | 4 | Operator support. |
| paul@6 | 5 | |
| paul@6 | 6 | Copyright (C) 2010, 2013, 2015, 2016 Paul Boddie <paul@boddie.org.uk> |
| paul@6 | 7 | |
| paul@6 | 8 | This program is free software; you can redistribute it and/or modify it under |
| paul@6 | 9 | the terms of the GNU General Public License as published by the Free Software |
| paul@6 | 10 | Foundation; either version 3 of the License, or (at your option) any later |
| paul@6 | 11 | version. |
| paul@6 | 12 | |
| paul@6 | 13 | This program is distributed in the hope that it will be useful, but WITHOUT |
| paul@6 | 14 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS |
| paul@6 | 15 | FOR A PARTICULAR PURPOSE. See the GNU General Public License for more |
| paul@6 | 16 | details. |
| paul@6 | 17 | |
| paul@6 | 18 | You should have received a copy of the GNU General Public License along with |
| paul@6 | 19 | this program. If not, see <http://www.gnu.org/licenses/>. |
| paul@6 | 20 | """ |
| paul@6 | 21 | |
| paul@6 | 22 | # Define "is" and "is not" in terms of native operations. They are imported by |
| paul@6 | 23 | # the operator.binary module. |
| paul@6 | 24 | |
| paul@354 | 25 | from native import is_, is_not |
| paul@6 | 26 | |
| paul@278 | 27 | def binary_op(a, b, left_accessor, right_accessor, default=None): |
| paul@6 | 28 | |
| paul@6 | 29 | """ |
| paul@6 | 30 | A single parameterised function providing the binary operator mechanism for |
| paul@6 | 31 | arguments 'a' and 'b' using accessors given as 'left_accessor' and |
| paul@6 | 32 | 'right_accessor' which provide the methods for the operands. |
| paul@6 | 33 | """ |
| paul@6 | 34 | |
| paul@6 | 35 | # First, try and get a method for the left argument, and then call it with |
| paul@6 | 36 | # the right argument. |
| paul@6 | 37 | |
| paul@6 | 38 | try: |
| paul@6 | 39 | fn = left_accessor(a) |
| paul@364 | 40 | except TypeError: |
| paul@6 | 41 | pass |
| paul@6 | 42 | else: |
| paul@6 | 43 | result = fn(b) |
| paul@6 | 44 | if is_not(result, NotImplemented): |
| paul@6 | 45 | return result |
| paul@6 | 46 | |
| paul@6 | 47 | # Otherwise, try and get a method for the right argument, and then call it |
| paul@6 | 48 | # with the left argument. |
| paul@6 | 49 | |
| paul@6 | 50 | try: |
| paul@6 | 51 | fn = right_accessor(b) |
| paul@364 | 52 | except TypeError: |
| paul@6 | 53 | pass |
| paul@6 | 54 | else: |
| paul@6 | 55 | result = fn(a) |
| paul@6 | 56 | if is_not(result, NotImplemented): |
| paul@6 | 57 | return result |
| paul@6 | 58 | |
| paul@6 | 59 | # Where no methods were available, or if neither method could support the |
| paul@278 | 60 | # operation, raise an exception or provide a default result. |
| paul@6 | 61 | |
| paul@278 | 62 | if default is None: |
| paul@278 | 63 | raise TypeError |
| paul@278 | 64 | else: |
| paul@278 | 65 | return default |
| paul@6 | 66 | |
| paul@278 | 67 | def unary_op(a, accessor, default=None): |
| paul@6 | 68 | |
| paul@6 | 69 | """ |
| paul@6 | 70 | A single parameterised function providing the unary operator mechanism for |
| paul@6 | 71 | the argument 'a' using the given 'accessor' to provide the method for the |
| paul@6 | 72 | operand. |
| paul@6 | 73 | """ |
| paul@6 | 74 | |
| paul@6 | 75 | # First, try and get a method for the argument, and then call it. |
| paul@6 | 76 | |
| paul@6 | 77 | try: |
| paul@6 | 78 | fn = accessor(a) |
| paul@364 | 79 | except TypeError: |
| paul@6 | 80 | pass |
| paul@6 | 81 | else: |
| paul@6 | 82 | result = fn() |
| paul@6 | 83 | if is_not(result, NotImplemented): |
| paul@6 | 84 | return result |
| paul@6 | 85 | |
| paul@6 | 86 | # Where no method was available, or if the method could not support the |
| paul@278 | 87 | # operation, raise an exception or provide a default result. |
| paul@6 | 88 | |
| paul@278 | 89 | if default is None: |
| paul@278 | 90 | raise TypeError |
| paul@278 | 91 | else: |
| paul@278 | 92 | return default |
| paul@6 | 93 | |
| paul@6 | 94 | def augassign(a, b, augmented_accessor, left_accessor, right_accessor): |
| paul@6 | 95 | |
| paul@6 | 96 | """ |
| paul@6 | 97 | A single parameterised function providing the augmented assignment mechanism |
| paul@6 | 98 | for arguments 'a' and 'b' either using 'augmented_accessor' (directly |
| paul@6 | 99 | affecting 'a') or using 'left_accessor' and 'right_accessor' (conventional |
| paul@6 | 100 | operator method accessors). |
| paul@6 | 101 | |
| paul@6 | 102 | The result of the assignment is returned. |
| paul@6 | 103 | """ |
| paul@6 | 104 | |
| paul@6 | 105 | # First, try and get a method that directly affects the assignment target. |
| paul@6 | 106 | |
| paul@6 | 107 | try: |
| paul@6 | 108 | fn = augmented_accessor(a) |
| paul@364 | 109 | except TypeError: |
| paul@6 | 110 | pass |
| paul@6 | 111 | else: |
| paul@6 | 112 | result = fn(b) |
| paul@6 | 113 | if is_not(result, NotImplemented): |
| paul@6 | 114 | return result |
| paul@6 | 115 | |
| paul@6 | 116 | # Otherwise, attempt a conventional binary operation. |
| paul@6 | 117 | |
| paul@6 | 118 | return binary_op(a, b, left_accessor, right_accessor) |
| paul@6 | 119 | |
| paul@6 | 120 | # vim: tabstop=4 expandtab shiftwidth=4 |
