recordtype

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220``` ```=========== recordtype =========== Overview ======== recordtype provides a factory function, named recordtype.recordtype. It is similar to collections.namedtuple, with the following differences: * recordtype instances are mutable. * recordtype supports per-field default values. * recordtype supports an optional default value, to be used by all fields do not have an explicit default value. Typical usage ============= You can use recordtype like a mutable namedtuple:: from recordtype import recordtype Point = recordtype('Point', 'x y') p = Point(1, 3) p.x = 2 assert p.x == 2 assert p.y == 3 Or, you can specify a default value for all fields:: Point = recordtype('Point', 'x y', default=3) p = Point(y=2) assert p.x == 3 assert p.y == 2 Or, you can specify per-field default values:: Point = recordtype('Point', [('x', 0), ('y', 100)]) p = Point() assert p.x == 0 assert p.y == 100 You can also specify a the per-field defaults with a mapping, instead of an interable. Note that this is only useful with an ordered mapping, such as an OrderedDict:: from collections import OrderedDict Point = recordtype('Point', OrderedDict((('y', 0), ('x', 100)))) p = Point() assert p.x == 100 assert p.y == 0 The default value will only be used if it is provided and a per-field default is not used:: Point = recordtype('Point', ['x', ('y', 100)], default=10) p = Point() assert p.x == 10 assert p.y == 100 If you use a mapping, the value NO_DEFAULT is convenient to specify that a field uses the default value:: from recordtype import NO_DEFAULT Point = recordtype('Point', OrderedDict((('y', NO_DEFAULT), ('x', 100))), default=5) p = Point() assert p.x == 100 assert p.y == 5 Creating types -------------- Specifying Fields ================= Fields can be specified as in namedtuple: as either a string specifing the field names, or as a iterable of field names. These two uses are equivalent:: Point = recordtype('Point', 'x y') Point = recordtype('Point', ['x', 'y']) If using a string, commas are first converted to spaces. So these are equivalent:: Point = recordtype('Point', 'x y') Point = recordtype('Point', 'x,y') Specifying Defaults =================== Per-field defaults can be specified by supplying a 2-tuple (name, default_value) instead of just a string for the field name. This is only supported when you specify a list of field names:: Point = recordtype('Point', [('x', 0), ('y', 0)]) p = Point(3) assert p.x == 3 assert p.y == 0 In addition to, or instead of, these per-field defaults, you can also specify a default value which is used when no per-field default value is specified:: Point = recordtype('Point', 'x y z', default=0) p = Point(y=3) assert p.x == 0 assert p.y == 3 assert p.z == 0 Point = recordtype('Point', [('x', 0), 'y', ('z', 0)], default=4) p = Point(z=2) assert p.x == 0 assert p.y == 4 assert p.z == 2 In addition to supplying the field names as an iterable of 2-tuples, you can also specify a mapping. The keys will be the field names, and the values will be the per-field default values. This is most useful with an OrderedDict, as the order of the fields will then be deterministic. The module variable NO_DEFAULT can be specified if you want a field to use the per-type default value instead of specifying it with a field:: Point = recordtype('Point', OrderedDict((('x', 0), ('y', NO_DEFAULT), ('z', 0), )), default=4) p = Point(z=2) assert p.x == 0 assert p.y == 4 assert p.z == 2 Writing to values ================= The objects retured by the factory function are fully writable, unlike the tuple-derived classes returned by namedtuple:: Point = recordtype('Point', 'x y') p = Point(1, 2) p.y = 4 assert p.x == 1 assert p.y == 4 Specifying __slots__ ==================== By default, the returned class sets __slots__, which is initialized to the field names. While this decreases memory usage by eliminating the instance dict, it also means that you cannot create new instance members. To change this behavior, specify use_slots=False when creating the recordtype:: Point = recordtype('Point', 'x y', use_slots=False) p = Point(0, 1) p.z = 2 assert p.x == 0 assert p.y == 1 assert p.z == 2 Additional class members ======================== recordtype classes contain these members: * _asdict(): Returns a dict which maps field names to their corresponding values. * _source: A string with the pure Python source code used to create the recordtype class. The source makes the recordtype self-documenting. It can be printed, executed using exec(), or saved to a file and imported. * _fields: Tuple of strings listing the field names. Useful for introspection. Renaming invalid field names ============================ This functionality is identical to namedtuple. If you specify rename=True, then any invalid field names are changed to _0, _1, etc. Reasons for a field name to be invalid are: * Zero length strings. * Containing characters other than alphanumerics and underscores. * A conflict with a Python reserved identifier. * Beginning with a digit. * Beginning with an underscore. * Using the same field name more than once. For example:: Point = recordtype('Point', 'x x for', rename=True) assert Point._fields == ('x', '_1', '_2') Creating and using instances ---------------------------- Because the type returned by recordtype is a normal Python class, you create instances as you would with any Python class. ```