/Doc/library/operator.rst
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1:mod:`operator` --- Standard operators as functions 2=================================================== 3 4.. module:: operator 5 :synopsis: Functions corresponding to the standard operators. 6.. sectionauthor:: Skip Montanaro <skip@automatrix.com> 7 8 9.. testsetup:: 10 11 import operator 12 from operator import itemgetter 13 14 15The :mod:`operator` module exports a set of functions implemented in C 16corresponding to the intrinsic operators of Python. For example, 17``operator.add(x, y)`` is equivalent to the expression ``x+y``. The function 18names are those used for special class methods; variants without leading and 19trailing ``__`` are also provided for convenience. 20 21The functions fall into categories that perform object comparisons, logical 22operations, mathematical operations, sequence operations, and abstract type 23tests. 24 25The object comparison functions are useful for all objects, and are named after 26the rich comparison operators they support: 27 28 29.. function:: lt(a, b) 30 le(a, b) 31 eq(a, b) 32 ne(a, b) 33 ge(a, b) 34 gt(a, b) 35 __lt__(a, b) 36 __le__(a, b) 37 __eq__(a, b) 38 __ne__(a, b) 39 __ge__(a, b) 40 __gt__(a, b) 41 42 Perform "rich comparisons" between *a* and *b*. Specifically, ``lt(a, b)`` is 43 equivalent to ``a < b``, ``le(a, b)`` is equivalent to ``a <= b``, ``eq(a, 44 b)`` is equivalent to ``a == b``, ``ne(a, b)`` is equivalent to ``a != b``, 45 ``gt(a, b)`` is equivalent to ``a > b`` and ``ge(a, b)`` is equivalent to ``a 46 >= b``. Note that unlike the built-in :func:`cmp`, these functions can 47 return any value, which may or may not be interpretable as a Boolean value. 48 See :ref:`comparisons` for more information about rich comparisons. 49 50 .. versionadded:: 2.2 51 52The logical operations are also generally applicable to all objects, and support 53truth tests, identity tests, and boolean operations: 54 55 56.. function:: not_(obj) 57 __not__(obj) 58 59 Return the outcome of :keyword:`not` *obj*. (Note that there is no 60 :meth:`__not__` method for object instances; only the interpreter core defines 61 this operation. The result is affected by the :meth:`__nonzero__` and 62 :meth:`__len__` methods.) 63 64 65.. function:: truth(obj) 66 67 Return :const:`True` if *obj* is true, and :const:`False` otherwise. This is 68 equivalent to using the :class:`bool` constructor. 69 70 71.. function:: is_(a, b) 72 73 Return ``a is b``. Tests object identity. 74 75 .. versionadded:: 2.3 76 77 78.. function:: is_not(a, b) 79 80 Return ``a is not b``. Tests object identity. 81 82 .. versionadded:: 2.3 83 84The mathematical and bitwise operations are the most numerous: 85 86 87.. function:: abs(obj) 88 __abs__(obj) 89 90 Return the absolute value of *obj*. 91 92 93.. function:: add(a, b) 94 __add__(a, b) 95 96 Return ``a + b``, for *a* and *b* numbers. 97 98 99.. function:: and_(a, b) 100 __and__(a, b) 101 102 Return the bitwise and of *a* and *b*. 103 104 105.. function:: div(a, b) 106 __div__(a, b) 107 108 Return ``a / b`` when ``__future__.division`` is not in effect. This is 109 also known as "classic" division. 110 111 112.. function:: floordiv(a, b) 113 __floordiv__(a, b) 114 115 Return ``a // b``. 116 117 .. versionadded:: 2.2 118 119 120.. function:: inv(obj) 121 invert(obj) 122 __inv__(obj) 123 __invert__(obj) 124 125 Return the bitwise inverse of the number *obj*. This is equivalent to ``~obj``. 126 127 .. versionadded:: 2.0 128 The names :func:`invert` and :func:`__invert__`. 129 130 131.. function:: lshift(a, b) 132 __lshift__(a, b) 133 134 Return *a* shifted left by *b*. 135 136 137.. function:: mod(a, b) 138 __mod__(a, b) 139 140 Return ``a % b``. 141 142 143.. function:: mul(a, b) 144 __mul__(a, b) 145 146 Return ``a * b``, for *a* and *b* numbers. 147 148 149.. function:: neg(obj) 150 __neg__(obj) 151 152 Return *obj* negated. 153 154 155.. function:: or_(a, b) 156 __or__(a, b) 157 158 Return the bitwise or of *a* and *b*. 159 160 161.. function:: pos(obj) 162 __pos__(obj) 163 164 Return *obj* positive. 165 166 167.. function:: pow(a, b) 168 __pow__(a, b) 169 170 Return ``a ** b``, for *a* and *b* numbers. 171 172 .. versionadded:: 2.3 173 174 175.. function:: rshift(a, b) 176 __rshift__(a, b) 177 178 Return *a* shifted right by *b*. 179 180 181.. function:: sub(a, b) 182 __sub__(a, b) 183 184 Return ``a - b``. 185 186 187.. function:: truediv(a, b) 188 __truediv__(a, b) 189 190 Return ``a / b`` when ``__future__.division`` is in effect. This is also 191 known as "true" division. 192 193 .. versionadded:: 2.2 194 195 196.. function:: xor(a, b) 197 __xor__(a, b) 198 199 Return the bitwise exclusive or of *a* and *b*. 200 201 202.. function:: index(a) 203 __index__(a) 204 205 Return *a* converted to an integer. Equivalent to ``a.__index__()``. 206 207 .. versionadded:: 2.5 208 209 210Operations which work with sequences include: 211 212.. function:: concat(a, b) 213 __concat__(a, b) 214 215 Return ``a + b`` for *a* and *b* sequences. 216 217 218.. function:: contains(a, b) 219 __contains__(a, b) 220 221 Return the outcome of the test ``b in a``. Note the reversed operands. 222 223 .. versionadded:: 2.0 224 The name :func:`__contains__`. 225 226 227.. function:: countOf(a, b) 228 229 Return the number of occurrences of *b* in *a*. 230 231 232.. function:: delitem(a, b) 233 __delitem__(a, b) 234 235 Remove the value of *a* at index *b*. 236 237 238.. function:: delslice(a, b, c) 239 __delslice__(a, b, c) 240 241 Delete the slice of *a* from index *b* to index *c-1*. 242 243 .. deprecated:: 2.6 244 This function is removed in Python 3.0. Use :func:`delitem` with a slice 245 index. 246 247 248.. function:: getitem(a, b) 249 __getitem__(a, b) 250 251 Return the value of *a* at index *b*. 252 253 254.. function:: getslice(a, b, c) 255 __getslice__(a, b, c) 256 257 Return the slice of *a* from index *b* to index *c-1*. 258 259 .. deprecated:: 2.6 260 This function is removed in Python 3.0. Use :func:`getitem` with a slice 261 index. 262 263 264.. function:: indexOf(a, b) 265 266 Return the index of the first of occurrence of *b* in *a*. 267 268 269.. function:: repeat(a, b) 270 __repeat__(a, b) 271 272 .. deprecated:: 2.6 273 This function is removed in Python 3.0. Use :func:`__mul__` instead. 274 275 Return ``a * b`` where *a* is a sequence and *b* is an integer. 276 277 278.. function:: sequenceIncludes(...) 279 280 .. deprecated:: 2.0 281 Use :func:`contains` instead. 282 283 Alias for :func:`contains`. 284 285 286.. function:: setitem(a, b, c) 287 __setitem__(a, b, c) 288 289 Set the value of *a* at index *b* to *c*. 290 291 292.. function:: setslice(a, b, c, v) 293 __setslice__(a, b, c, v) 294 295 Set the slice of *a* from index *b* to index *c-1* to the sequence *v*. 296 297 .. deprecated:: 2.6 298 This function is removed in Python 3.0. Use :func:`setitem` with a slice 299 index. 300 301Example use of operator functions:: 302 303 >>> # Elementwise multiplication 304 >>> map(mul, [0, 1, 2, 3], [10, 20, 30, 40]) 305 [0, 20, 60, 120] 306 307 >>> # Dot product 308 >>> sum(map(mul, [0, 1, 2, 3], [10, 20, 30, 40])) 309 200 310 311Many operations have an "in-place" version. The following functions provide a 312more primitive access to in-place operators than the usual syntax does; for 313example, the :term:`statement` ``x += y`` is equivalent to 314``x = operator.iadd(x, y)``. Another way to put it is to say that 315``z = operator.iadd(x, y)`` is equivalent to the compound statement 316``z = x; z += y``. 317 318.. function:: iadd(a, b) 319 __iadd__(a, b) 320 321 ``a = iadd(a, b)`` is equivalent to ``a += b``. 322 323 .. versionadded:: 2.5 324 325 326.. function:: iand(a, b) 327 __iand__(a, b) 328 329 ``a = iand(a, b)`` is equivalent to ``a &= b``. 330 331 .. versionadded:: 2.5 332 333 334.. function:: iconcat(a, b) 335 __iconcat__(a, b) 336 337 ``a = iconcat(a, b)`` is equivalent to ``a += b`` for *a* and *b* sequences. 338 339 .. versionadded:: 2.5 340 341 342.. function:: idiv(a, b) 343 __idiv__(a, b) 344 345 ``a = idiv(a, b)`` is equivalent to ``a /= b`` when ``__future__.division`` is 346 not in effect. 347 348 .. versionadded:: 2.5 349 350 351.. function:: ifloordiv(a, b) 352 __ifloordiv__(a, b) 353 354 ``a = ifloordiv(a, b)`` is equivalent to ``a //= b``. 355 356 .. versionadded:: 2.5 357 358 359.. function:: ilshift(a, b) 360 __ilshift__(a, b) 361 362 ``a = ilshift(a, b)`` is equivalent to ``a <``\ ``<= b``. 363 364 .. versionadded:: 2.5 365 366 367.. function:: imod(a, b) 368 __imod__(a, b) 369 370 ``a = imod(a, b)`` is equivalent to ``a %= b``. 371 372 .. versionadded:: 2.5 373 374 375.. function:: imul(a, b) 376 __imul__(a, b) 377 378 ``a = imul(a, b)`` is equivalent to ``a *= b``. 379 380 .. versionadded:: 2.5 381 382 383.. function:: ior(a, b) 384 __ior__(a, b) 385 386 ``a = ior(a, b)`` is equivalent to ``a |= b``. 387 388 .. versionadded:: 2.5 389 390 391.. function:: ipow(a, b) 392 __ipow__(a, b) 393 394 ``a = ipow(a, b)`` is equivalent to ``a **= b``. 395 396 .. versionadded:: 2.5 397 398 399.. function:: irepeat(a, b) 400 __irepeat__(a, b) 401 402 .. deprecated:: 2.6 403 This function is removed in Python 3.0. Use :func:`__imul__` instead. 404 405 ``a = irepeat(a, b)`` is equivalent to ``a *= b`` where *a* is a sequence and 406 *b* is an integer. 407 408 .. versionadded:: 2.5 409 410 411.. function:: irshift(a, b) 412 __irshift__(a, b) 413 414 ``a = irshift(a, b)`` is equivalent to ``a >>= b``. 415 416 .. versionadded:: 2.5 417 418 419.. function:: isub(a, b) 420 __isub__(a, b) 421 422 ``a = isub(a, b)`` is equivalent to ``a -= b``. 423 424 .. versionadded:: 2.5 425 426 427.. function:: itruediv(a, b) 428 __itruediv__(a, b) 429 430 ``a = itruediv(a, b)`` is equivalent to ``a /= b`` when ``__future__.division`` 431 is in effect. 432 433 .. versionadded:: 2.5 434 435 436.. function:: ixor(a, b) 437 __ixor__(a, b) 438 439 ``a = ixor(a, b)`` is equivalent to ``a ^= b``. 440 441 .. versionadded:: 2.5 442 443 444The :mod:`operator` module also defines a few predicates to test the type of 445objects; however, these are not all reliable. It is preferable to test 446abstract base classes instead (see :mod:`collections` and 447:mod:`numbers` for details). 448 449.. function:: isCallable(obj) 450 451 .. deprecated:: 2.0 452 Use ``isinstance(x, collections.Callable)`` instead. 453 454 Returns true if the object *obj* can be called like a function, otherwise it 455 returns false. True is returned for functions, bound and unbound methods, class 456 objects, and instance objects which support the :meth:`__call__` method. 457 458 459.. function:: isMappingType(obj) 460 461 .. deprecated:: 2.6 462 This function is removed in Python 3.0. Use ``isinstance(x, collections.Mapping)`` instead. 463 464 Returns true if the object *obj* supports the mapping interface. This is true for 465 dictionaries and all instance objects defining :meth:`__getitem__`. 466 467 468.. function:: isNumberType(obj) 469 470 .. deprecated:: 2.6 471 This function is removed in Python 3.0. Use ``isinstance(x, numbers.Number)`` instead. 472 473 Returns true if the object *obj* represents a number. This is true for all 474 numeric types implemented in C. 475 476 477.. function:: isSequenceType(obj) 478 479 .. deprecated:: 2.6 480 This function is removed in Python 3.0. Use ``isinstance(x, collections.Sequence)`` instead. 481 482 Returns true if the object *obj* supports the sequence protocol. This returns true 483 for all objects which define sequence methods in C, and for all instance objects 484 defining :meth:`__getitem__`. 485 486 487The :mod:`operator` module also defines tools for generalized attribute and item 488lookups. These are useful for making fast field extractors as arguments for 489:func:`map`, :func:`sorted`, :meth:`itertools.groupby`, or other functions that 490expect a function argument. 491 492 493.. function:: attrgetter(attr[, args...]) 494 495 Return a callable object that fetches *attr* from its operand. If more than one 496 attribute is requested, returns a tuple of attributes. After, 497 ``f = attrgetter('name')``, the call ``f(b)`` returns ``b.name``. After, 498 ``f = attrgetter('name', 'date')``, the call ``f(b)`` returns ``(b.name, 499 b.date)``. 500 501 The attribute names can also contain dots; after ``f = attrgetter('date.month')``, 502 the call ``f(b)`` returns ``b.date.month``. 503 504 .. versionadded:: 2.4 505 506 .. versionchanged:: 2.5 507 Added support for multiple attributes. 508 509 .. versionchanged:: 2.6 510 Added support for dotted attributes. 511 512 513.. function:: itemgetter(item[, args...]) 514 515 Return a callable object that fetches *item* from its operand using the 516 operand's :meth:`__getitem__` method. If multiple items are specified, 517 returns a tuple of lookup values. Equivalent to:: 518 519 def itemgetter(*items): 520 if len(items) == 1: 521 item = items[0] 522 def g(obj): 523 return obj[item] 524 else: 525 def g(obj): 526 return tuple(obj[item] for item in items) 527 return g 528 529 The items can be any type accepted by the operand's :meth:`__getitem__` 530 method. Dictionaries accept any hashable value. Lists, tuples, and 531 strings accept an index or a slice: 532 533 >>> itemgetter(1)('ABCDEFG') 534 'B' 535 >>> itemgetter(1,3,5)('ABCDEFG') 536 ('B', 'D', 'F') 537 >>> itemgetter(slice(2,None))('ABCDEFG') 538 'CDEFG' 539 540 .. versionadded:: 2.4 541 542 .. versionchanged:: 2.5 543 Added support for multiple item extraction. 544 545 Example of using :func:`itemgetter` to retrieve specific fields from a 546 tuple record: 547 548 >>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)] 549 >>> getcount = itemgetter(1) 550 >>> map(getcount, inventory) 551 [3, 2, 5, 1] 552 >>> sorted(inventory, key=getcount) 553 [('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)] 554 555 556.. function:: methodcaller(name[, args...]) 557 558 Return a callable object that calls the method *name* on its operand. If 559 additional arguments and/or keyword arguments are given, they will be given 560 to the method as well. After ``f = methodcaller('name')``, the call ``f(b)`` 561 returns ``b.name()``. After ``f = methodcaller('name', 'foo', bar=1)``, the 562 call ``f(b)`` returns ``b.name('foo', bar=1)``. 563 564 .. versionadded:: 2.6 565 566 567.. _operator-map: 568 569Mapping Operators to Functions 570------------------------------ 571 572This table shows how abstract operations correspond to operator symbols in the 573Python syntax and the functions in the :mod:`operator` module. 574 575+-----------------------+-------------------------+---------------------------------+ 576| Operation | Syntax | Function | 577+=======================+=========================+=================================+ 578| Addition | ``a + b`` | ``add(a, b)`` | 579+-----------------------+-------------------------+---------------------------------+ 580| Concatenation | ``seq1 + seq2`` | ``concat(seq1, seq2)`` | 581+-----------------------+-------------------------+---------------------------------+ 582| Containment Test | ``obj in seq`` | ``contains(seq, obj)`` | 583+-----------------------+-------------------------+---------------------------------+ 584| Division | ``a / b`` | ``div(a, b)`` (without | 585| | | ``__future__.division``) | 586+-----------------------+-------------------------+---------------------------------+ 587| Division | ``a / b`` | ``truediv(a, b)`` (with | 588| | | ``__future__.division``) | 589+-----------------------+-------------------------+---------------------------------+ 590| Division | ``a // b`` | ``floordiv(a, b)`` | 591+-----------------------+-------------------------+---------------------------------+ 592| Bitwise And | ``a & b`` | ``and_(a, b)`` | 593+-----------------------+-------------------------+---------------------------------+ 594| Bitwise Exclusive Or | ``a ^ b`` | ``xor(a, b)`` | 595+-----------------------+-------------------------+---------------------------------+ 596| Bitwise Inversion | ``~ a`` | ``invert(a)`` | 597+-----------------------+-------------------------+---------------------------------+ 598| Bitwise Or | ``a | b`` | ``or_(a, b)`` | 599+-----------------------+-------------------------+---------------------------------+ 600| Exponentiation | ``a ** b`` | ``pow(a, b)`` | 601+-----------------------+-------------------------+---------------------------------+ 602| Identity | ``a is b`` | ``is_(a, b)`` | 603+-----------------------+-------------------------+---------------------------------+ 604| Identity | ``a is not b`` | ``is_not(a, b)`` | 605+-----------------------+-------------------------+---------------------------------+ 606| Indexed Assignment | ``obj[k] = v`` | ``setitem(obj, k, v)`` | 607+-----------------------+-------------------------+---------------------------------+ 608| Indexed Deletion | ``del obj[k]`` | ``delitem(obj, k)`` | 609+-----------------------+-------------------------+---------------------------------+ 610| Indexing | ``obj[k]`` | ``getitem(obj, k)`` | 611+-----------------------+-------------------------+---------------------------------+ 612| Left Shift | ``a << b`` | ``lshift(a, b)`` | 613+-----------------------+-------------------------+---------------------------------+ 614| Modulo | ``a % b`` | ``mod(a, b)`` | 615+-----------------------+-------------------------+---------------------------------+ 616| Multiplication | ``a * b`` | ``mul(a, b)`` | 617+-----------------------+-------------------------+---------------------------------+ 618| Negation (Arithmetic) | ``- a`` | ``neg(a)`` | 619+-----------------------+-------------------------+---------------------------------+ 620| Negation (Logical) | ``not a`` | ``not_(a)`` | 621+-----------------------+-------------------------+---------------------------------+ 622| Right Shift | ``a >> b`` | ``rshift(a, b)`` | 623+-----------------------+-------------------------+---------------------------------+ 624| Sequence Repetition | ``seq * i`` | ``repeat(seq, i)`` | 625+-----------------------+-------------------------+---------------------------------+ 626| Slice Assignment | ``seq[i:j] = values`` | ``setslice(seq, i, j, values)`` | 627+-----------------------+-------------------------+---------------------------------+ 628| Slice Deletion | ``del seq[i:j]`` | ``delslice(seq, i, j)`` | 629+-----------------------+-------------------------+---------------------------------+ 630| Slicing | ``seq[i:j]`` | ``getslice(seq, i, j)`` | 631+-----------------------+-------------------------+---------------------------------+ 632| String Formatting | ``s % obj`` | ``mod(s, obj)`` | 633+-----------------------+-------------------------+---------------------------------+ 634| Subtraction | ``a - b`` | ``sub(a, b)`` | 635+-----------------------+-------------------------+---------------------------------+ 636| Truth Test | ``obj`` | ``truth(obj)`` | 637+-----------------------+-------------------------+---------------------------------+ 638| Ordering | ``a < b`` | ``lt(a, b)`` | 639+-----------------------+-------------------------+---------------------------------+ 640| Ordering | ``a <= b`` | ``le(a, b)`` | 641+-----------------------+-------------------------+---------------------------------+ 642| Equality | ``a == b`` | ``eq(a, b)`` | 643+-----------------------+-------------------------+---------------------------------+ 644| Difference | ``a != b`` | ``ne(a, b)`` | 645+-----------------------+-------------------------+---------------------------------+ 646| Ordering | ``a >= b`` | ``ge(a, b)`` | 647+-----------------------+-------------------------+---------------------------------+ 648| Ordering | ``a > b`` | ``gt(a, b)`` | 649+-----------------------+-------------------------+---------------------------------+ 650