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 efficient functions corresponding to 16the intrinsic operators of Python. For example, ``operator.add(x, y)`` is 17equivalent to the expression ``x+y``. The function names are those used for 18special class methods; variants without leading and trailing ``__`` are also 19provided 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:: index(a) 121 __index__(a) 122 123 Return *a* converted to an integer. Equivalent to ``a.__index__()``. 124 125 .. versionadded:: 2.5 126 127 128.. function:: inv(obj) 129 invert(obj) 130 __inv__(obj) 131 __invert__(obj) 132 133 Return the bitwise inverse of the number *obj*. This is equivalent to ``~obj``. 134 135 .. versionadded:: 2.0 136 The names :func:`invert` and :func:`__invert__`. 137 138 139.. function:: lshift(a, b) 140 __lshift__(a, b) 141 142 Return *a* shifted left by *b*. 143 144 145.. function:: mod(a, b) 146 __mod__(a, b) 147 148 Return ``a % b``. 149 150 151.. function:: mul(a, b) 152 __mul__(a, b) 153 154 Return ``a * b``, for *a* and *b* numbers. 155 156 157.. function:: neg(obj) 158 __neg__(obj) 159 160 Return *obj* negated (``-obj``). 161 162 163.. function:: or_(a, b) 164 __or__(a, b) 165 166 Return the bitwise or of *a* and *b*. 167 168 169.. function:: pos(obj) 170 __pos__(obj) 171 172 Return *obj* positive (``+obj``). 173 174 175.. function:: pow(a, b) 176 __pow__(a, b) 177 178 Return ``a ** b``, for *a* and *b* numbers. 179 180 .. versionadded:: 2.3 181 182 183.. function:: rshift(a, b) 184 __rshift__(a, b) 185 186 Return *a* shifted right by *b*. 187 188 189.. function:: sub(a, b) 190 __sub__(a, b) 191 192 Return ``a - b``. 193 194 195.. function:: truediv(a, b) 196 __truediv__(a, b) 197 198 Return ``a / b`` when ``__future__.division`` is in effect. This is also 199 known as "true" division. 200 201 .. versionadded:: 2.2 202 203 204.. function:: xor(a, b) 205 __xor__(a, b) 206 207 Return the bitwise exclusive or of *a* and *b*. 208 209 210Operations which work with sequences (some of them with mappings too) 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.x. 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.x. 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:: 2.7 273 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.x. 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:: 2.7 403 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:: 2.7 462 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:: 2.7 471 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:: 2.7 480 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) 494 attrgetter(*attrs) 495 496 Return a callable object that fetches *attr* from its operand. 497 If more than one attribute is requested, returns a tuple of attributes. 498 The attribute names can also contain dots. For example: 499 500 * After ``f = attrgetter('name')``, the call ``f(b)`` returns ``b.name``. 501 502 * After ``f = attrgetter('name', 'date')``, the call ``f(b)`` returns 503 ``(b.name, b.date)``. 504 505 * After ``f = attrgetter('name.first', 'name.last')``, the call ``f(b)`` 506 returns ``(b.name.first, b.name.last)``. 507 508 Equivalent to:: 509 510 def attrgetter(*items): 511 if len(items) == 1: 512 attr = items[0] 513 def g(obj): 514 return resolve_attr(obj, attr) 515 else: 516 def g(obj): 517 return tuple(resolve_attr(obj, attr) for attr in items) 518 return g 519 520 def resolve_attr(obj, attr): 521 for name in attr.split("."): 522 obj = getattr(obj, name) 523 return obj 524 525 526 .. versionadded:: 2.4 527 528 .. versionchanged:: 2.5 529 Added support for multiple attributes. 530 531 .. versionchanged:: 2.6 532 Added support for dotted attributes. 533 534 535.. function:: itemgetter(item) 536 itemgetter(*items) 537 538 Return a callable object that fetches *item* from its operand using the 539 operand's :meth:`__getitem__` method. If multiple items are specified, 540 returns a tuple of lookup values. For example: 541 542 * After ``f = itemgetter(2)``, the call ``f(r)`` returns ``r[2]``. 543 544 * After ``g = itemgetter(2, 5, 3)``, the call ``g(r)`` returns 545 ``(r[2], r[5], r[3])``. 546 547 Equivalent to:: 548 549 def itemgetter(*items): 550 if len(items) == 1: 551 item = items[0] 552 def g(obj): 553 return obj[item] 554 else: 555 def g(obj): 556 return tuple(obj[item] for item in items) 557 return g 558 559 The items can be any type accepted by the operand's :meth:`__getitem__` 560 method. Dictionaries accept any hashable value. Lists, tuples, and 561 strings accept an index or a slice: 562 563 >>> itemgetter(1)('ABCDEFG') 564 'B' 565 >>> itemgetter(1,3,5)('ABCDEFG') 566 ('B', 'D', 'F') 567 >>> itemgetter(slice(2,None))('ABCDEFG') 568 'CDEFG' 569 570 .. versionadded:: 2.4 571 572 .. versionchanged:: 2.5 573 Added support for multiple item extraction. 574 575 Example of using :func:`itemgetter` to retrieve specific fields from a 576 tuple record: 577 578 >>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)] 579 >>> getcount = itemgetter(1) 580 >>> map(getcount, inventory) 581 [3, 2, 5, 1] 582 >>> sorted(inventory, key=getcount) 583 [('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)] 584 585 586.. function:: methodcaller(name[, args...]) 587 588 Return a callable object that calls the method *name* on its operand. If 589 additional arguments and/or keyword arguments are given, they will be given 590 to the method as well. For example: 591 592 * After ``f = methodcaller('name')``, the call ``f(b)`` returns ``b.name()``. 593 594 * After ``f = methodcaller('name', 'foo', bar=1)``, the call ``f(b)`` 595 returns ``b.name('foo', bar=1)``. 596 597 Equivalent to:: 598 599 def methodcaller(name, *args, **kwargs): 600 def caller(obj): 601 return getattr(obj, name)(*args, **kwargs) 602 return caller 603 604 .. versionadded:: 2.6 605 606 607.. _operator-map: 608 609Mapping Operators to Functions 610------------------------------ 611 612This table shows how abstract operations correspond to operator symbols in the 613Python syntax and the functions in the :mod:`operator` module. 614 615+-----------------------+-------------------------+---------------------------------------+ 616| Operation | Syntax | Function | 617+=======================+=========================+=======================================+ 618| Addition | ``a + b`` | ``add(a, b)`` | 619+-----------------------+-------------------------+---------------------------------------+ 620| Concatenation | ``seq1 + seq2`` | ``concat(seq1, seq2)`` | 621+-----------------------+-------------------------+---------------------------------------+ 622| Containment Test | ``obj in seq`` | ``contains(seq, obj)`` | 623+-----------------------+-------------------------+---------------------------------------+ 624| Division | ``a / b`` | ``div(a, b)`` (without | 625| | | ``__future__.division``) | 626+-----------------------+-------------------------+---------------------------------------+ 627| Division | ``a / b`` | ``truediv(a, b)`` (with | 628| | | ``__future__.division``) | 629+-----------------------+-------------------------+---------------------------------------+ 630| Division | ``a // b`` | ``floordiv(a, b)`` | 631+-----------------------+-------------------------+---------------------------------------+ 632| Bitwise And | ``a & b`` | ``and_(a, b)`` | 633+-----------------------+-------------------------+---------------------------------------+ 634| Bitwise Exclusive Or | ``a ^ b`` | ``xor(a, b)`` | 635+-----------------------+-------------------------+---------------------------------------+ 636| Bitwise Inversion | ``~ a`` | ``invert(a)`` | 637+-----------------------+-------------------------+---------------------------------------+ 638| Bitwise Or | ``a | b`` | ``or_(a, b)`` | 639+-----------------------+-------------------------+---------------------------------------+ 640| Exponentiation | ``a ** b`` | ``pow(a, b)`` | 641+-----------------------+-------------------------+---------------------------------------+ 642| Identity | ``a is b`` | ``is_(a, b)`` | 643+-----------------------+-------------------------+---------------------------------------+ 644| Identity | ``a is not b`` | ``is_not(a, b)`` | 645+-----------------------+-------------------------+---------------------------------------+ 646| Indexed Assignment | ``obj[k] = v`` | ``setitem(obj, k, v)`` | 647+-----------------------+-------------------------+---------------------------------------+ 648| Indexed Deletion | ``del obj[k]`` | ``delitem(obj, k)`` | 649+-----------------------+-------------------------+---------------------------------------+ 650| Indexing | ``obj[k]`` | ``getitem(obj, k)`` | 651+-----------------------+-------------------------+---------------------------------------+ 652| Left Shift | ``a << b`` | ``lshift(a, b)`` | 653+-----------------------+-------------------------+---------------------------------------+ 654| Modulo | ``a % b`` | ``mod(a, b)`` | 655+-----------------------+-------------------------+---------------------------------------+ 656| Multiplication | ``a * b`` | ``mul(a, b)`` | 657+-----------------------+-------------------------+---------------------------------------+ 658| Negation (Arithmetic) | ``- a`` | ``neg(a)`` | 659+-----------------------+-------------------------+---------------------------------------+ 660| Negation (Logical) | ``not a`` | ``not_(a)`` | 661+-----------------------+-------------------------+---------------------------------------+ 662| Positive | ``+ a`` | ``pos(a)`` | 663+-----------------------+-------------------------+---------------------------------------+ 664| Right Shift | ``a >> b`` | ``rshift(a, b)`` | 665+-----------------------+-------------------------+---------------------------------------+ 666| Sequence Repetition | ``seq * i`` | ``repeat(seq, i)`` | 667+-----------------------+-------------------------+---------------------------------------+ 668| Slice Assignment | ``seq[i:j] = values`` | ``setitem(seq, slice(i, j), values)`` | 669+-----------------------+-------------------------+---------------------------------------+ 670| Slice Deletion | ``del seq[i:j]`` | ``delitem(seq, slice(i, j))`` | 671+-----------------------+-------------------------+---------------------------------------+ 672| Slicing | ``seq[i:j]`` | ``getitem(seq, slice(i, j))`` | 673+-----------------------+-------------------------+---------------------------------------+ 674| String Formatting | ``s % obj`` | ``mod(s, obj)`` | 675+-----------------------+-------------------------+---------------------------------------+ 676| Subtraction | ``a - b`` | ``sub(a, b)`` | 677+-----------------------+-------------------------+---------------------------------------+ 678| Truth Test | ``obj`` | ``truth(obj)`` | 679+-----------------------+-------------------------+---------------------------------------+ 680| Ordering | ``a < b`` | ``lt(a, b)`` | 681+-----------------------+-------------------------+---------------------------------------+ 682| Ordering | ``a <= b`` | ``le(a, b)`` | 683+-----------------------+-------------------------+---------------------------------------+ 684| Equality | ``a == b`` | ``eq(a, b)`` | 685+-----------------------+-------------------------+---------------------------------------+ 686| Difference | ``a != b`` | ``ne(a, b)`` | 687+-----------------------+-------------------------+---------------------------------------+ 688| Ordering | ``a >= b`` | ``ge(a, b)`` | 689+-----------------------+-------------------------+---------------------------------------+ 690| Ordering | ``a > b`` | ``gt(a, b)`` | 691+-----------------------+-------------------------+---------------------------------------+ 692 693