1 #!/usr/bin/env python 2 3 """ 4 Sequence operations. 5 6 Copyright (C) 2015, 2016 Paul Boddie <paul@boddie.org.uk> 7 8 This program is free software; you can redistribute it and/or modify it under 9 the terms of the GNU General Public License as published by the Free Software 10 Foundation; either version 3 of the License, or (at your option) any later 11 version. 12 13 This program is distributed in the hope that it will be useful, but WITHOUT 14 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 15 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more 16 details. 17 18 You should have received a copy of the GNU General Public License along with 19 this program. If not, see <http://www.gnu.org/licenses/>. 20 """ 21 22 from native import _isinstance 23 24 class sequence: 25 26 "A common base class for sequence types." 27 28 def _str(self, opening, closing): 29 30 "Serialise this object with the given 'opening' and 'closing' strings." 31 32 b = buffer() 33 i = 0 34 l = self.__len__() 35 first = True 36 37 b.append(opening) 38 while i < l: 39 if first: 40 first = False 41 else: 42 b.append(", ") 43 b.append(repr(self.__get_single_item__(i))) 44 i += 1 45 b.append(closing) 46 47 return str(b) 48 49 def __getitem__(self, index): 50 51 "Return the item or slice specified by 'index'." 52 53 # Normalise any integer indexes, converting negative indexes to positive 54 # ones. 55 56 if _isinstance(index, int): 57 index = _normalise_index(index, self.__len__()) 58 return self.__get_single_item__(index) 59 60 # Handle slices separately. 61 62 elif _isinstance(index, slice): 63 return self.__getslice__(index.start, index.end) 64 65 # No other kinds of objects are supported as indexes. 66 67 else: 68 raise TypeError 69 70 def __setitem__(self, index, value): 71 72 "Set at 'index' the given 'value'." 73 74 # Normalise any integer indexes, converting negative indexes to positive 75 # ones. 76 77 if _isinstance(index, int): 78 index = _normalise_index(index, self.__len__()) 79 return self.__set_single_item__(index, value) 80 81 # Handle slices separately. 82 83 elif _isinstance(index, slice): 84 return self.__setslice__(index.start, index.end, value) 85 86 # No other kinds of objects are supported as indexes. 87 88 else: 89 raise TypeError 90 91 def __getslice__(self, start, end=None): 92 93 "Return a slice starting from 'start', with the optional 'end'." 94 95 length = self.__len__() 96 97 # Handle a null start as the first position, otherwise normalising any 98 # start index. 99 100 if start is None: 101 start = 0 102 else: 103 start = _normalise_index(start, length) 104 105 # Handle a null end as the first position after the end of the sequence, 106 # otherwise normalising any end index. 107 108 if end is None: 109 end = length 110 else: 111 end = _normalise_index(end, length) 112 113 result = [] 114 115 while start < end: 116 result.append(self.__get_single_item__(start)) 117 start += 1 118 119 return result 120 121 def _get_absolute_index(index, length): 122 123 """ 124 Return the absolute index for 'index' given a collection having the 125 specified 'length'. 126 """ 127 128 if index < 0: 129 return length + index 130 else: 131 return index 132 133 def _normalise_index(index, length): 134 135 "Normalise 'index' for a collection having the specified 'length'." 136 137 return _min(length, _max(0, _get_absolute_index(index, length))) 138 139 def _max(x, y): 140 141 "Return the maximum of 'x' and 'y'." 142 143 if x >= y: 144 return x 145 else: 146 return y 147 148 def _min(x, y): 149 150 "Return the minimum of 'x' and 'y'." 151 152 if x <= y: 153 return x 154 else: 155 return y 156 157 def _tuple(l): pass 158 159 # vim: tabstop=4 expandtab shiftwidth=4