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GeezerVison is showing github.com — PythonPEPS/pep-0249.txt at main · BrentMat/PythonPEPS Expand file tree/ Copy pathpep-0249.txtMore file actions 1373 lines (958 loc) · 45.3 KB / Copy pathpep-0249.txtFile metadata and controls1373 lines (958 loc) · 45.3 KB 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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 PEP: 249 Title: Python Database API Specification v2.0 Author: Marc-André Lemburg <[email protected]> Discussions-To: [email protected] Status: Final Type: Informational Content-Type: text/x-rst Created: 12-Apr-1999 Post-History: Replaces: 248 Introduction ============ This API has been defined to encourage similarity between the Python modules that are used to access databases. By doing this, we hope to achieve a consistency leading to more easily understood modules, code that is generally more portable across databases, and a broader reach of database connectivity from Python. Comments and questions about this specification may be directed to the `SIG for Database Interfacing with Python <[email protected]>`__. For more information on database interfacing with Python and available packages see the `Database Topic Guide <http://www.python.org/topics/database/>`__. This document describes the Python Database API Specification 2.0 and a set of common optional extensions. The previous version 1.0 version is still available as reference, in :PEP:`248`. Package writers are encouraged to use this version of the specification as basis for new interfaces. Module Interface ================= Constructors ------------ Access to the database is made available through connection objects. The module must provide the following constructor for these: .. _connect: `connect`_\ ( *parameters...* ) Constructor for creating a connection to the database. Returns a Connection_ Object. It takes a number of parameters which are database dependent. [1]_ Globals ------- These module globals must be defined: .. _apilevel: `apilevel`_ String constant stating the supported DB API level. Currently only the strings "``1.0``" and "``2.0``" are allowed. If not given, a DB-API 1.0 level interface should be assumed. .. _threadsafety: `threadsafety`_ Integer constant stating the level of thread safety the interface supports. Possible values are: ============ ======================================================= threadsafety Meaning ============ ======================================================= 0 Threads may not share the module. 1 Threads may share the module, but not connections. 2 Threads may share the module and connections. 3 Threads may share the module, connections and cursors. ============ ======================================================= Sharing in the above context means that two threads may use a resource without wrapping it using a mutex semaphore to implement resource locking. Note that you cannot always make external resources thread safe by managing access using a mutex: the resource may rely on global variables or other external sources that are beyond your control. .. _paramstyle: `paramstyle`_ String constant stating the type of parameter marker formatting expected by the interface. Possible values are [2]_: ============ ============================================================== paramstyle Meaning ============ ============================================================== ``qmark`` Question mark style, e.g. ``...WHERE name=?`` ``numeric`` Numeric, positional style, e.g. ``...WHERE name=:1`` ``named`` Named style, e.g. ``...WHERE name=:name`` ``format`` ANSI C printf format codes, e.g. ``...WHERE name=%s`` ``pyformat`` Python extended format codes, e.g. ``...WHERE name=%(name)s`` ============ ============================================================== Exceptions ---------- The module should make all error information available through these exceptions or subclasses thereof: .. _Warning: `Warning`_ Exception raised for important warnings like data truncations while inserting, etc. It must be a subclass of the Python ``Exception`` class [10]_ [11]_. .. _Error: `Error`_ Exception that is the base class of all other error exceptions. You can use this to catch all errors with one single ``except`` statement. Warnings are not considered errors and thus should not use this class as base. It must be a subclass of the Python ``Exception`` class [10]_. .. _InterfaceError: `InterfaceError`_ Exception raised for errors that are related to the database interface rather than the database itself. It must be a subclass of Error_. .. _DatabaseError: `DatabaseError`_ Exception raised for errors that are related to the database. It must be a subclass of Error_. .. _DataError: `DataError`_ Exception raised for errors that are due to problems with the processed data like division by zero, numeric value out of range, etc. It must be a subclass of DatabaseError_. .. _OperationalError: `OperationalError`_ Exception raised for errors that are related to the database's operation and not necessarily under the control of the programmer, e.g. an unexpected disconnect occurs, the data source name is not found, a transaction could not be processed, a memory allocation error occurred during processing, etc. It must be a subclass of DatabaseError_. .. _IntegrityError: `IntegrityError`_ Exception raised when the relational integrity of the database is affected, e.g. a foreign key check fails. It must be a subclass of DatabaseError_. .. _InternalError: `InternalError`_ Exception raised when the database encounters an internal error, e.g. the cursor is not valid anymore, the transaction is out of sync, etc. It must be a subclass of DatabaseError_. .. _ProgrammingError: `ProgrammingError`_ Exception raised for programming errors, e.g. table not found or already exists, syntax error in the SQL statement, wrong number of parameters specified, etc. It must be a subclass of DatabaseError_. .. _NotSupportedError: `NotSupportedError`_ Exception raised in case a method or database API was used which is not supported by the database, e.g. requesting a `.rollback()`_ on a connection that does not support transaction or has transactions turned off. It must be a subclass of DatabaseError_. This is the exception inheritance layout [10]_ [11]_: .. code-block:: text Exception |__Warning |__Error |__InterfaceError |__DatabaseError |__DataError |__OperationalError |__IntegrityError |__InternalError |__ProgrammingError |__NotSupportedError .. Note:: The values of these exceptions are not defined. They should give the user a fairly good idea of what went wrong, though. .. _Connection: Connection Objects ================== Connection objects should respond to the following methods. Connection methods ------------------ .. .close(): .. _Connection.close: `.close() <#Connection.close>`_ Close the connection now (rather than whenever ``.__del__()`` is called). The connection will be unusable from this point forward; an Error_ (or subclass) exception will be raised if any operation is attempted with the connection. The same applies to all cursor objects trying to use the connection. Note that closing a connection without committing the changes first will cause an implicit rollback to be performed. .. _.commit: .. _.commit(): `.commit`_\ () Commit any pending transaction to the database. Note that if the database supports an auto-commit feature, this must be initially off. An interface method may be provided to turn it back on. Database modules that do not support transactions should implement this method with void functionality. .. _.rollback: .. _.rollback(): `.rollback`_\ () This method is optional since not all databases provide transaction support. [3]_ In case a database does provide transactions this method causes the database to roll back to the start of any pending transaction. Closing a connection without committing the changes first will cause an implicit rollback to be performed. .. _.cursor: `.cursor`_\ () Return a new Cursor_ Object using the connection. If the database does not provide a direct cursor concept, the module will have to emulate cursors using other means to the extent needed by this specification. [4]_ .. _Cursor: Cursor Objects ============== These objects represent a database cursor, which is used to manage the context of a fetch operation. Cursors created from the same connection are not isolated, *i.e.*, any changes done to the database by a cursor are immediately visible by the other cursors. Cursors created from different connections can or can not be isolated, depending on how the transaction support is implemented (see also the connection's `.rollback`_\ () and `.commit`_\ () methods). Cursor Objects should respond to the following methods and attributes. Cursor attributes ----------------- .. _.description: `.description`_ This read-only attribute is a sequence of 7-item sequences. Each of these sequences contains information describing one result column: * ``name`` * ``type_code`` * ``display_size`` * ``internal_size`` * ``precision`` * ``scale`` * ``null_ok`` The first two items (``name`` and ``type_code``) are mandatory, the other five are optional and are set to ``None`` if no meaningful values can be provided. This attribute will be ``None`` for operations that do not return rows or if the cursor has not had an operation invoked via the `.execute*()`_ method yet. The ``type_code`` can be interpreted by comparing it to the `Type Objects`_ specified in the section below. .. _.rowcount: `.rowcount`_ This read-only attribute specifies the number of rows that the last `.execute*()`_ produced (for DQL statements like ``SELECT``) or affected (for DML statements like ``UPDATE`` or ``INSERT``). [9]_ The attribute is -1 in case no `.execute*()`_ has been performed on the cursor or the rowcount of the last operation is cannot be determined by the interface. [7]_ .. note:: Future versions of the DB API specification could redefine the latter case to have the object return ``None`` instead of -1. Cursor methods -------------- .. _.callproc: .. _.callproc(): `.callproc`_\ ( *procname* [, *parameters* ] ) (This method is optional since not all databases provide stored procedures. [3]_) Call a stored database procedure with the given name. The sequence of parameters must contain one entry for each argument that the procedure expects. The result of the call is returned as modified copy of the input sequence. Input parameters are left untouched, output and input/output parameters replaced with possibly new values. The procedure may also provide a result set as output. This must then be made available through the standard `.fetch*()`_ methods. .. .close: .. _Cursor.close: .. _Cursor.close(): `.close <#Cursor.close>`_\ () Close the cursor now (rather than whenever ``__del__`` is called). The cursor will be unusable from this point forward; an Error_ (or subclass) exception will be raised if any operation is attempted with the cursor. .. _.execute*: .. _.execute*(): .. _.execute: .. _.execute(): `.execute`_\ (*operation* [, *parameters*]) Prepare and execute a database operation (query or command). Parameters may be provided as sequence or mapping and will be bound to variables in the operation. Variables are specified in a database-specific notation (see the module's paramstyle_ attribute for details). [5]_ A reference to the operation will be retained by the cursor. If the same operation object is passed in again, then the cursor can optimize its behavior. This is most effective for algorithms where the same operation is used, but different parameters are bound to it (many times). For maximum efficiency when reusing an operation, it is best to use the `.setinputsizes()`_ method to specify the parameter types and sizes ahead of time. It is legal for a parameter to not match the predefined information; the implementation should compensate, possibly with a loss of efficiency. The parameters may also be specified as list of tuples to e.g. insert multiple rows in a single operation, but this kind of usage is deprecated: `.executemany()`_ should be used instead. Return values are not defined. .. _.executemany: .. _.executemany(): `.executemany`_\ ( *operation*, *seq_of_parameters* ) Prepare a database operation (query or command) and then execute it against all parameter sequences or mappings found in the sequence *seq_of_parameters*. Modules are free to implement this method using multiple calls to the `.execute()`_ method or by using array operations to have the database process the sequence as a whole in one call. Use of this method for an operation which produces one or more result sets constitutes undefined behavior, and the implementation is permitted (but not required) to raise an exception when it detects that a result set has been created by an invocation of the operation. The same comments as for `.execute()`_ also apply accordingly to this method. Return values are not defined. .. _.fetch*: .. _.fetch*(): .. _.fetchone: .. _.fetchone(): `.fetchone`_\ () Fetch the next row of a query result set, returning a single sequence, or ``None`` when no more data is available. [6]_ An Error_ (or subclass) exception is raised if the previous call to `.execute*()`_ did not produce any result set or no call was issued yet. .. _.fetchmany: .. _.fetchmany(): `.fetchmany`_\ ([*size=cursor.arraysize*]) Fetch the next set of rows of a query result, returning a sequence of sequences (e.g. a list of tuples). An empty sequence is returned when no more rows are available. The number of rows to fetch per call is specified by the parameter. If it is not given, the cursor's arraysize determines the number of rows to be fetched. The method should try to fetch as many rows as indicated by the size parameter. If this is not possible due to the specified number of rows not being available, fewer rows may be returned. An Error_ (or subclass) exception is raised if the previous call to `.execute*()`_ did not produce any result set or no call was issued yet. Note there are performance considerations involved with the *size* parameter. For optimal performance, it is usually best to use the `.arraysize`_ attribute. If the size parameter is used, then it is best for it to retain the same value from one `.fetchmany()`_ call to the next. .. _.fetchall: .. _.fetchall(): `.fetchall`_\ () Fetch all (remaining) rows of a query result, returning them as a sequence of sequences (e.g. a list of tuples). Note that the cursor's arraysize attribute can affect the performance of this operation. An Error_ (or subclass) exception is raised if the previous call to `.execute*()`_ did not produce any result set or no call was issued yet. .. _.nextset: .. _.nextset(): `.nextset`_\ () (This method is optional since not all databases support multiple result sets. [3]_) This method will make the cursor skip to the next available set, discarding any remaining rows from the current set. If there are no more sets, the method returns ``None``. Otherwise, it returns a true value and subsequent calls to the `.fetch*()`_ methods will return rows from the next result set. An Error_ (or subclass) exception is raised if the previous call to `.execute*()`_ did not produce any result set or no call was issued yet. .. _.arraysize: `.arraysize`_ This read/write attribute specifies the number of rows to fetch at a time with `.fetchmany()`_. It defaults to 1 meaning to fetch a single row at a time. Implementations must observe this value with respect to the `.fetchmany()`_ method, but are free to interact with the database a single row at a time. It may also be used in the implementation of `.executemany()`_. .. _.setinputsizes: .. _.setinputsizes(): `.setinputsizes`_\ (*sizes*) This can be used before a call to `.execute*()`_ to predefine memory areas for the operation's parameters. *sizes* is specified as a sequence — one item for each input parameter. The item should be a Type Object that corresponds to the input that will be used, or it should be an integer specifying the maximum length of a string parameter. If the item is ``None``, then no predefined memory area will be reserved for that column (this is useful to avoid predefined areas for large inputs). This method would be used before the `.execute*()`_ method is invoked. Implementations are free to have this method do nothing and users are free to not use it. .. _.setoutputsize: .. _.setoutputsize(): `.setoutputsize`_\ (*size* [, *column*]) Set a column buffer size for fetches of large columns (e.g. ``LONG``\s, ``BLOB``\s, etc.). The column is specified as an index into the result sequence. Not specifying the column will set the default size for all large columns in the cursor. This method would be used before the `.execute*()`_ method is invoked. Implementations are free to have this method do nothing and users are free to not use it. .. _Type Objects: Type Objects and Constructors ============================= Many databases need to have the input in a particular format for binding to an operation's input parameters. For example, if an input is destined for a ``DATE`` column, then it must be bound to the database in a particular string format. Similar problems exist for "Row ID" columns or large binary items (e.g. blobs or ``RAW`` columns). This presents problems for Python since the parameters to the `.execute*()`_ method are untyped. When the database module sees a Python string object, it doesn't know if it should be bound as a simple ``CHAR`` column, as a raw ``BINARY`` item, or as a ``DATE``. To overcome this problem, a module must provide the constructors defined below to create objects that can hold special values. When passed to the cursor methods, the module can then detect the proper type of the input parameter and bind it accordingly. A Cursor_ Object's description attribute returns information about each of the result columns of a query. The ``type_code`` must compare equal to one of Type Objects defined below. Type Objects may be equal to more than one type code (e.g. ``DATETIME`` could be equal to the type codes for date, time and timestamp columns; see the `Implementation Hints`_ below for details). The module exports the following constructors and singletons: .. _Date: `Date`_\ (*year*, *month*, *day*) This function constructs an object holding a date value. .. _Time: `Time`_\ (*hour*, *minute*, *second*) This function constructs an object holding a time value. .. _Timestamp: `Timestamp`_\ (*year*, *month*, *day*, *hour*, *minute*, *second*) This function constructs an object holding a time stamp value. .. _DateFromTicks: `DateFromTicks`_\ (*ticks*) This function constructs an object holding a date value from the given ticks value (number of seconds since the epoch; see the documentation of `the standard Python time module <http://docs.python.org/library/time.html>`__ for details). .. _TimeFromTicks: `TimeFromTicks`_\ (*ticks*) This function constructs an object holding a time value from the given ticks value (number of seconds since the epoch; see the documentation of the standard Python time module for details). .. _TimeStampFromTicks: `TimestampFromTicks`_\ (*ticks*) This function constructs an object holding a time stamp value from the given ticks value (number of seconds since the epoch; see the documentation of the standard Python time module for details). .. _Binary: `Binary`_\ (*string*) This function constructs an object capable of holding a binary (long) string value. .. _STRING: `STRING`_ type This type object is used to describe columns in a database that are string-based (e.g. ``CHAR``). .. _Binary type: `BINARY`_ type This type object is used to describe (long) binary columns in a database (e.g. ``LONG``, ``RAW``, ``BLOB``\s). .. _NUMBER: `NUMBER`_ type This type object is used to describe numeric columns in a database. .. _DATETIME: `DATETIME`_ type This type object is used to describe date/time columns in a database. .. _ROWID: `ROWID`_ type This type object is used to describe the "Row ID" column in a database. SQL ``NULL`` values are represented by the Python ``None`` singleton on input and output. .. Note:: Usage of Unix ticks for database interfacing can cause troubles because of the limited date range they cover. .. _Implementation Hints: Implementation Hints for Module Authors ======================================= * Date/time objects can be implemented as `Python datetime module <http://docs.python.org/library/datetime.html>`__ objects (available since Python 2.3, with a C API since 2.4) or using the `mxDateTime <http://www.egenix.com/products/python/mxBase/mxDateTime/>`_ package (available for all Python versions since 1.5.2). They both provide all necessary constructors and methods at Python and C level. * Here is a sample implementation of the Unix ticks based constructors for date/time delegating work to the generic constructors:: import time def DateFromTicks(ticks): return Date(*time.localtime(ticks)[:3]) def TimeFromTicks(ticks): return Time(*time.localtime(ticks)[3:6]) def TimestampFromTicks(ticks): return Timestamp(*time.localtime(ticks)[:6]) * The preferred object type for Binary objects are the buffer types available in standard Python starting with version 1.5.2. Please see the Python documentation for details. For information about the C interface have a look at ``Include/bufferobject.h`` and ``Objects/bufferobject.c`` in the Python source distribution. * This Python class allows implementing the above type objects even though the description type code field yields multiple values for on type object:: class DBAPITypeObject: def __init__(self,*values): self.values = values def __cmp__(self,other): if other in self.values: return 0 if other < self.values: return 1 else: return -1 The resulting type object compares equal to all values passed to the constructor. * Here is a snippet of Python code that implements the exception hierarchy defined above [10]_:: class Error(Exception): pass class Warning(Exception): pass class InterfaceError(Error): pass class DatabaseError(Error): pass class InternalError(DatabaseError): pass class OperationalError(DatabaseError): pass class ProgrammingError(DatabaseError): pass class IntegrityError(DatabaseError): pass class DataError(DatabaseError): pass class NotSupportedError(DatabaseError): pass In C you can use the ``PyErr_NewException(fullname, base, NULL)`` API to create the exception objects. Optional DB API Extensions ========================== During the lifetime of DB API 2.0, module authors have often extended their implementations beyond what is required by this DB API specification. To enhance compatibility and to provide a clean upgrade path to possible future versions of the specification, this section defines a set of common extensions to the core DB API 2.0 specification. As with all DB API optional features, the database module authors are free to not implement these additional attributes and methods (using them will then result in an ``AttributeError``) or to raise a NotSupportedError_ in case the availability can only be checked at run-time. It has been proposed to make usage of these extensions optionally visible to the programmer by issuing Python warnings through the Python warning framework. To make this feature useful, the warning messages must be standardized in order to be able to mask them. These standard messages are referred to below as *Warning Message*. .. _.rownumber: Cursor\ `.rownumber`_ This read-only attribute should provide the current 0-based index of the cursor in the result set or ``None`` if the index cannot be determined. The index can be seen as index of the cursor in a sequence (the result set). The next fetch operation will fetch the row indexed by `.rownumber`_ in that sequence. *Warning Message:* "DB-API extension cursor.rownumber used" .. _Connection.Error: .. _Connection.ProgrammingError: `Connection.Error`_, `Connection.ProgrammingError`_, etc. All exception classes defined by the DB API standard should be exposed on the Connection_ objects as attributes (in addition to being available at module scope). These attributes simplify error handling in multi-connection environments. *Warning Message:* "DB-API extension connection.<exception> used" .. _.connection: Cursor\ `.connection`_ This read-only attribute return a reference to the Connection_ object on which the cursor was created. The attribute simplifies writing polymorph code in multi-connection environments. *Warning Message:* "DB-API extension cursor.connection used" .. _.scroll: .. _.scroll(): Cursor\ `.scroll`_\ (*value* [, *mode='relative'* ]) Scroll the cursor in the result set to a new position according to *mode*. If mode is ``relative`` (default), value is taken as offset to the current position in the result set, if set to ``absolute``, value states an absolute target position. An ``IndexError`` should be raised in case a scroll operation would leave the result set. In this case, the cursor position is left undefined (ideal would be to not move the cursor at all). .. Note:: This method should use native scrollable cursors, if available, or revert to an emulation for forward-only scrollable cursors. The method may raise NotSupportedError_ to signal that a specific operation is not supported by the database (e.g. backward scrolling). *Warning Message:* "DB-API extension cursor.scroll() used" .. _Cursor.messages: `Cursor.messages`_ This is a Python list object to which the interface appends tuples (exception class, exception value) for all messages which the interfaces receives from the underlying database for this cursor. The list is cleared by all standard cursor methods calls (prior to executing the call) except for the `.fetch*()`_ calls automatically to avoid excessive memory usage and can also be cleared by executing ``del cursor.messages[:]``. All error and warning messages generated by the database are placed into this list, so checking the list allows the user to verify correct operation of the method calls. The aim of this attribute is to eliminate the need for a Warning exception which often causes problems (some warnings really only have informational character). *Warning Message:* "DB-API extension cursor.messages used" .. _Connection.messages: `Connection.messages`_ Same as Cursor.messages_ except that the messages in the list are connection oriented. The list is cleared automatically by all standard connection methods calls (prior to executing the call) to avoid excessive memory usage and can also be cleared by executing ``del connection.messages[:]``. *Warning Message:* "DB-API extension connection.messages used" .. _.next: .. _.next(): Cursor\ `.next`_\ () Return the next row from the currently executing SQL statement using the same semantics as `.fetchone()`_. A ``StopIteration`` exception is raised when the result set is exhausted for Python versions 2.2 and later. Previous versions don't have the ``StopIteration`` exception and so the method should raise an ``IndexError`` instead. *Warning Message:* "DB-API extension cursor.next() used" .. _.__iter__: .. _.__iter__(): Cursor\ `.__iter__`_\ () Return self to make cursors compatible to the iteration protocol [8]_. *Warning Message:* "DB-API extension cursor.__iter__() used" .. _.lastrowid: Cursor\ `.lastrowid`_ This read-only attribute provides the rowid of the last modified row (most databases return a rowid only when a single ``INSERT`` operation is performed). If the operation does not set a rowid or if the database does not support rowids, this attribute should be set to ``None``. The semantics of ``.lastrowid`` are undefined in case the last executed statement modified more than one row, e.g. when using ``INSERT`` with ``.executemany()``. *Warning Message:* "DB-API extension cursor.lastrowid used" .. _Connection.autocommit: .. _.autocommit: Connection\ `.autocommit`_ Attribute to query and set the autocommit mode of the connection. Return ``True`` if the connection is operating in autocommit (non- transactional) mode. Return ``False`` if the connection is operating in manual commit (transactional) mode. Setting the attribute to ``True`` or ``False`` adjusts the connection's mode accordingly. Changing the setting from ``True`` to ``False`` (disabling autocommit) will have the database leave autocommit mode and start a new transaction. Changing from ``False`` to ``True`` (enabling autocommit) has database dependent semantics with respect to how pending transactions are handled. [12]_ *Deprecation notice*: Even though several database modules implement both the read and write nature of this attribute, setting the autocommit mode by writing to the attribute is deprecated, since this may result in I/O and related exceptions, making it difficult to implement in an async context. [13]_ *Warning Message:* "DB-API extension connection.autocommit used" Optional Error Handling Extensions ================================== The core DB API specification only introduces a set of exceptions which can be raised to report errors to the user. In some cases, exceptions may be too disruptive for the flow of a program or even render execution impossible. For these cases and in order to simplify error handling when dealing with databases, database module authors may choose to implement user definable error handlers. This section describes a standard way of defining these error handlers. .. _Connection.errorhandler: .. _Cursor.errorhandler: `Connection.errorhandler`_, `Cursor.errorhandler`_ Read/write attribute which references an error handler to call in case an error condition is met. The handler must be a Python callable taking the following arguments: .. parsed-literal:: errorhandler(*connection*, *cursor*, *errorclass*, *errorvalue*) where connection is a reference to the connection on which the cursor operates, cursor a reference to the cursor (or ``None`` in case the error does not apply to a cursor), *errorclass* is an error class which to instantiate using *errorvalue* as construction argument. The standard error handler should add the error information to the appropriate ``.messages`` attribute (`Connection.messages`_ or `Cursor.messages`_) and raise the exception defined by the given *errorclass* and *errorvalue* parameters. If no ``.errorhandler`` is set (the attribute is ``None``), the |
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