lexical_analysis.rst 26.3 KB
Newer Older
1 2 3 4 5 6 7

.. _lexical:

****************
Lexical analysis
****************

8
.. index:: lexical analysis, parser, token
9 10 11 12 13

A Python program is read by a *parser*.  Input to the parser is a stream of
*tokens*, generated by the *lexical analyzer*.  This chapter describes how the
lexical analyzer breaks a file into tokens.

14 15 16 17
Python reads program text as Unicode code points; the encoding of a source file
can be given by an encoding declaration and defaults to UTF-8, see :pep:`3120`
for details.  If the source file cannot be decoded, a :exc:`SyntaxError` is
raised.
18 19 20 21 22 23 24


.. _line-structure:

Line structure
==============

25
.. index:: line structure
26 27 28 29

A Python program is divided into a number of *logical lines*.


30
.. _logical-lines:
31 32 33 34

Logical lines
-------------

35
.. index:: logical line, physical line, line joining, NEWLINE token
36 37 38 39 40 41 42 43

The end of a logical line is represented by the token NEWLINE.  Statements
cannot cross logical line boundaries except where NEWLINE is allowed by the
syntax (e.g., between statements in compound statements). A logical line is
constructed from one or more *physical lines* by following the explicit or
implicit *line joining* rules.


44
.. _physical-lines:
45 46 47 48 49 50 51

Physical lines
--------------

A physical line is a sequence of characters terminated by an end-of-line
sequence.  In source files, any of the standard platform line termination
sequences can be used - the Unix form using ASCII LF (linefeed), the Windows
52
form using the ASCII sequence CR LF (return followed by linefeed), or the old
53 54 55 56 57 58 59 60 61 62 63 64 65
Macintosh form using the ASCII CR (return) character.  All of these forms can be
used equally, regardless of platform.

When embedding Python, source code strings should be passed to Python APIs using
the standard C conventions for newline characters (the ``\n`` character,
representing ASCII LF, is the line terminator).


.. _comments:

Comments
--------

66
.. index:: comment, hash character
67 68 69 70 71 72 73 74 75 76 77 78

A comment starts with a hash character (``#``) that is not part of a string
literal, and ends at the end of the physical line.  A comment signifies the end
of the logical line unless the implicit line joining rules are invoked. Comments
are ignored by the syntax; they are not tokens.


.. _encodings:

Encoding declarations
---------------------

79
.. index:: source character set, encodings
80 81 82 83 84 85 86 87 88 89 90 91

If a comment in the first or second line of the Python script matches the
regular expression ``coding[=:]\s*([-\w.]+)``, this comment is processed as an
encoding declaration; the first group of this expression names the encoding of
the source code file. The recommended forms of this expression are ::

   # -*- coding: <encoding-name> -*-

which is recognized also by GNU Emacs, and ::

   # vim:fileencoding=<encoding-name>

92 93 94 95 96 97
which is recognized by Bram Moolenaar's VIM.

If no encoding declaration is found, the default encoding is UTF-8.  In
addition, if the first bytes of the file are the UTF-8 byte-order mark
(``b'\xef\xbb\xbf'``), the declared file encoding is UTF-8 (this is supported,
among others, by Microsoft's :program:`notepad`).
98 99

If an encoding is declared, the encoding name must be recognized by Python. The
100 101
encoding is used for all lexical analysis, including string literals, comments
and identifiers. The encoding declaration must appear on a line of its own.
102

103
.. XXX there should be a list of supported encodings.
104 105 106 107 108 109 110


.. _explicit-joining:

Explicit line joining
---------------------

111
.. index:: physical line, line joining, line continuation, backslash character
112 113 114 115 116

Two or more physical lines may be joined into logical lines using backslash
characters (``\``), as follows: when a physical line ends in a backslash that is
not part of a string literal or comment, it is joined with the following forming
a single logical line, deleting the backslash and the following end-of-line
117
character.  For example::
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

   if 1900 < year < 2100 and 1 <= month <= 12 \
      and 1 <= day <= 31 and 0 <= hour < 24 \
      and 0 <= minute < 60 and 0 <= second < 60:   # Looks like a valid date
           return 1

A line ending in a backslash cannot carry a comment.  A backslash does not
continue a comment.  A backslash does not continue a token except for string
literals (i.e., tokens other than string literals cannot be split across
physical lines using a backslash).  A backslash is illegal elsewhere on a line
outside a string literal.


.. _implicit-joining:

Implicit line joining
---------------------

Expressions in parentheses, square brackets or curly braces can be split over
more than one physical line without using backslashes. For example::

   month_names = ['Januari', 'Februari', 'Maart',      # These are the
                  'April',   'Mei',      'Juni',       # Dutch names
                  'Juli',    'Augustus', 'September',  # for the months
                  'Oktober', 'November', 'December']   # of the year

Implicitly continued lines can carry comments.  The indentation of the
continuation lines is not important.  Blank continuation lines are allowed.
There is no NEWLINE token between implicit continuation lines.  Implicitly
continued lines can also occur within triple-quoted strings (see below); in that
case they cannot carry comments.


.. _blank-lines:

Blank lines
-----------

.. index:: single: blank line

A logical line that contains only spaces, tabs, formfeeds and possibly a
comment, is ignored (i.e., no NEWLINE token is generated).  During interactive
input of statements, handling of a blank line may differ depending on the
161 162 163
implementation of the read-eval-print loop.  In the standard interactive
interpreter, an entirely blank logical line (i.e. one containing not even
whitespace or a comment) terminates a multi-line statement.
164 165 166 167 168 169 170


.. _indentation:

Indentation
-----------

171
.. index:: indentation, leading whitespace, space, tab, grouping, statement grouping
172 173 174 175 176

Leading whitespace (spaces and tabs) at the beginning of a logical line is used
to compute the indentation level of the line, which in turn is used to determine
the grouping of statements.

177 178 179 180 181 182
Tabs are replaced (from left to right) by one to eight spaces such that the
total number of characters up to and including the replacement is a multiple of
eight (this is intended to be the same rule as used by Unix).  The total number
of spaces preceding the first non-blank character then determines the line's
indentation.  Indentation cannot be split over multiple physical lines using
backslashes; the whitespace up to the first backslash determines the
183 184
indentation.

185 186 187 188
Indentation is rejected as inconsistent if a source file mixes tabs and spaces
in a way that makes the meaning dependent on the worth of a tab in spaces; a
:exc:`TabError` is raised in that case.

189 190 191 192 193 194 195 196 197 198
**Cross-platform compatibility note:** because of the nature of text editors on
non-UNIX platforms, it is unwise to use a mixture of spaces and tabs for the
indentation in a single source file.  It should also be noted that different
platforms may explicitly limit the maximum indentation level.

A formfeed character may be present at the start of the line; it will be ignored
for the indentation calculations above.  Formfeed characters occurring elsewhere
in the leading whitespace have an undefined effect (for instance, they may reset
the space count to zero).

199
.. index:: INDENT token, DEDENT token
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

The indentation levels of consecutive lines are used to generate INDENT and
DEDENT tokens, using a stack, as follows.

Before the first line of the file is read, a single zero is pushed on the stack;
this will never be popped off again.  The numbers pushed on the stack will
always be strictly increasing from bottom to top.  At the beginning of each
logical line, the line's indentation level is compared to the top of the stack.
If it is equal, nothing happens. If it is larger, it is pushed on the stack, and
one INDENT token is generated.  If it is smaller, it *must* be one of the
numbers occurring on the stack; all numbers on the stack that are larger are
popped off, and for each number popped off a DEDENT token is generated.  At the
end of the file, a DEDENT token is generated for each number remaining on the
stack that is larger than zero.

Here is an example of a correctly (though confusingly) indented piece of Python
code::

   def perm(l):
           # Compute the list of all permutations of l
       if len(l) <= 1:
                     return [l]
       r = []
       for i in range(len(l)):
                s = l[:i] + l[i+1:]
                p = perm(s)
                for x in p:
                 r.append(l[i:i+1] + x)
       return r

The following example shows various indentation errors::

    def perm(l):                       # error: first line indented
   for i in range(len(l)):             # error: not indented
       s = l[:i] + l[i+1:]
           p = perm(l[:i] + l[i+1:])   # error: unexpected indent
           for x in p:
                   r.append(l[i:i+1] + x)
               return r                # error: inconsistent dedent

(Actually, the first three errors are detected by the parser; only the last
error is found by the lexical analyzer --- the indentation of ``return r`` does
not match a level popped off the stack.)


.. _whitespace:

Whitespace between tokens
-------------------------

Except at the beginning of a logical line or in string literals, the whitespace
characters space, tab and formfeed can be used interchangeably to separate
tokens.  Whitespace is needed between two tokens only if their concatenation
could otherwise be interpreted as a different token (e.g., ab is one token, but
a b is two tokens).


.. _other-tokens:

Other tokens
============

Besides NEWLINE, INDENT and DEDENT, the following categories of tokens exist:
*identifiers*, *keywords*, *literals*, *operators*, and *delimiters*. Whitespace
characters (other than line terminators, discussed earlier) are not tokens, but
serve to delimit tokens. Where ambiguity exists, a token comprises the longest
possible string that forms a legal token, when read from left to right.


.. _identifiers:

Identifiers and keywords
========================

274
.. index:: identifier, name
275 276

Identifiers (also referred to as *names*) are described by the following lexical
277
definitions.
278

279
The syntax of identifiers in Python is based on the Unicode standard annex
280 281
UAX-31, with elaboration and changes as defined below; see also :pep:`3131` for
further details.
282 283

Within the ASCII range (U+0001..U+007F), the valid characters for identifiers
284 285 286 287 288 289 290
are the same as in Python 2.x: the uppercase and lowercase letters ``A`` through
``Z``, the underscore ``_`` and, except for the first character, the digits
``0`` through ``9``.

Python 3.0 introduces additional characters from outside the ASCII range (see
:pep:`3131`).  For these characters, the classification uses the version of the
Unicode Character Database as included in the :mod:`unicodedata` module.
291 292 293

Identifiers are unlimited in length.  Case is significant.

294 295
.. productionlist::
   identifier: `id_start` `id_continue`*
296 297
   id_start: <all characters in general categories Lu, Ll, Lt, Lm, Lo, Nl, the underscore, and characters with the Other_ID_Start property>
   id_continue: <all characters in `id_start`, plus characters in the categories Mn, Mc, Nd, Pc and others with the Other_ID_Continue property>
298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317

The Unicode category codes mentioned above stand for:

* *Lu* - uppercase letters
* *Ll* - lowercase letters
* *Lt* - titlecase letters
* *Lm* - modifier letters
* *Lo* - other letters
* *Nl* - letter numbers
* *Mn* - nonspacing marks
* *Mc* - spacing combining marks
* *Nd* - decimal numbers
* *Pc* - connector punctuations

All identifiers are converted into the normal form NFC while parsing; comparison
of identifiers is based on NFC.

A non-normative HTML file listing all valid identifier characters for Unicode
4.1 can be found at
http://www.dcl.hpi.uni-potsdam.de/home/loewis/table-3131.html.
318

319

320 321 322 323 324 325 326 327 328 329 330
.. _keywords:

Keywords
--------

.. index::
   single: keyword
   single: reserved word

The following identifiers are used as reserved words, or *keywords* of the
language, and cannot be used as ordinary identifiers.  They must be spelled
331 332 333
exactly as written here:

.. sourcecode:: text
334

335 336 337 338 339 340 341
   False      class      finally    is         return
   None       continue   for        lambda     try
   True       def        from       nonlocal   while
   and        del        global     not        with
   as         elif       if         or         yield
   assert     else       import     pass
   break      except     in         raise
342 343 344 345 346 347 348 349 350 351 352 353 354

.. _id-classes:

Reserved classes of identifiers
-------------------------------

Certain classes of identifiers (besides keywords) have special meanings.  These
classes are identified by the patterns of leading and trailing underscore
characters:

``_*``
   Not imported by ``from module import *``.  The special identifier ``_`` is used
   in the interactive interpreter to store the result of the last evaluation; it is
355
   stored in the :mod:`builtins` module.  When not in interactive mode, ``_``
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
   has no special meaning and is not defined. See section :ref:`import`.

   .. note::

      The name ``_`` is often used in conjunction with internationalization;
      refer to the documentation for the :mod:`gettext` module for more
      information on this convention.

``__*__``
   System-defined names.  These names are defined by the interpreter and its
   implementation (including the standard library); applications should not expect
   to define additional names using this convention.  The set of names of this
   class defined by Python may be extended in future versions. See section
   :ref:`specialnames`.

``__*``
   Class-private names.  Names in this category, when used within the context of a
   class definition, are re-written to use a mangled form to help avoid name
   clashes between "private" attributes of base and derived classes. See section
   :ref:`atom-identifiers`.


.. _literals:

Literals
========

383
.. index:: literal, constant
384 385 386 387 388 389

Literals are notations for constant values of some built-in types.


.. _strings:

390 391
String and Bytes literals
-------------------------
392

393
.. index:: string literal, bytes literal, ASCII
394 395 396 397 398

String literals are described by the following lexical definitions:

.. productionlist::
   stringliteral: [`stringprefix`](`shortstring` | `longstring`)
399
   stringprefix: "r" | "R"
400
   shortstring: "'" `shortstringitem`* "'" | '"' `shortstringitem`* '"'
401 402 403
   longstring: "'''" `longstringitem`* "'''" | '"""' `longstringitem`* '"""'
   shortstringitem: `shortstringchar` | `stringescapeseq`
   longstringitem: `longstringchar` | `stringescapeseq`
404 405
   shortstringchar: <any source character except "\" or newline or the quote>
   longstringchar: <any source character except "\">
406 407 408 409 410 411 412 413 414 415 416 417
   stringescapeseq: "\" <any source character>

.. productionlist::
   bytesliteral: `bytesprefix`(`shortbytes` | `longbytes`)
   bytesprefix: "b" | "B"
   shortbytes: "'" `shortbytesitem`* "'" | '"' `shortbytesitem`* '"'
   longbytes: "'''" `longbytesitem`* "'''" | '"""' `longbytesitem`* '"""'
   shortbytesitem: `shortbyteschar` | `bytesescapeseq`
   longbytesitem: `longbyteschar` | `bytesescapeseq`
   shortbyteschar: <any ASCII character except "\" or newline or the quote>
   longbyteschar: <any ASCII character except "\">
   bytesescapeseq: "\" <any ASCII character>
418 419

One syntactic restriction not indicated by these productions is that whitespace
420 421 422 423
is not allowed between the :token:`stringprefix` or :token:`bytesprefix` and the
rest of the literal. The source character set is defined by the encoding
declaration; it is UTF-8 if no encoding declaration is given in the source file;
see section :ref:`encodings`.
424

425
.. index:: triple-quoted string, Unicode Consortium, raw string
426

427
In plain English: Both types of literals can be enclosed in matching single quotes
428 429 430 431
(``'``) or double quotes (``"``).  They can also be enclosed in matching groups
of three single or double quotes (these are generally referred to as
*triple-quoted strings*).  The backslash (``\``) character is used to escape
characters that otherwise have a special meaning, such as newline, backslash
432 433 434
itself, or the quote character.

String literals may optionally be prefixed with a letter ``'r'`` or ``'R'``;
435 436 437
such strings are called :dfn:`raw strings` and treat backslashes as literal
characters.  As a result, ``'\U'`` and ``'\u'`` escapes in raw strings are not
treated specially.
438 439 440 441 442

Bytes literals are always prefixed with ``'b'`` or ``'B'``; they produce an
instance of the :class:`bytes` type instead of the :class:`str` type.  They
may only contain ASCII characters; bytes with a numeric value of 128 or greater
must be expressed with escapes.
443 444 445 446 447

In triple-quoted strings, unescaped newlines and quotes are allowed (and are
retained), except that three unescaped quotes in a row terminate the string.  (A
"quote" is the character used to open the string, i.e. either ``'`` or ``"``.)

448
.. index:: physical line, escape sequence, Standard C, C
449 450 451 452 453 454 455 456

Unless an ``'r'`` or ``'R'`` prefix is present, escape sequences in strings are
interpreted according to rules similar to those used by Standard C.  The
recognized escape sequences are:

+-----------------+---------------------------------+-------+
| Escape Sequence | Meaning                         | Notes |
+=================+=================================+=======+
457
| ``\newline``    | Backslash and newline ignored   |       |
458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478
+-----------------+---------------------------------+-------+
| ``\\``          | Backslash (``\``)               |       |
+-----------------+---------------------------------+-------+
| ``\'``          | Single quote (``'``)            |       |
+-----------------+---------------------------------+-------+
| ``\"``          | Double quote (``"``)            |       |
+-----------------+---------------------------------+-------+
| ``\a``          | ASCII Bell (BEL)                |       |
+-----------------+---------------------------------+-------+
| ``\b``          | ASCII Backspace (BS)            |       |
+-----------------+---------------------------------+-------+
| ``\f``          | ASCII Formfeed (FF)             |       |
+-----------------+---------------------------------+-------+
| ``\n``          | ASCII Linefeed (LF)             |       |
+-----------------+---------------------------------+-------+
| ``\r``          | ASCII Carriage Return (CR)      |       |
+-----------------+---------------------------------+-------+
| ``\t``          | ASCII Horizontal Tab (TAB)      |       |
+-----------------+---------------------------------+-------+
| ``\v``          | ASCII Vertical Tab (VT)         |       |
+-----------------+---------------------------------+-------+
479
| ``\ooo``        | Character with octal value      | (1,3) |
480 481
|                 | *ooo*                           |       |
+-----------------+---------------------------------+-------+
482
| ``\xhh``        | Character with hex value *hh*   | (2,3) |
483 484
+-----------------+---------------------------------+-------+

485 486 487 488 489 490 491 492 493 494 495 496 497 498
Escape sequences only recognized in string literals are:

+-----------------+---------------------------------+-------+
| Escape Sequence | Meaning                         | Notes |
+=================+=================================+=======+
| ``\N{name}``    | Character named *name* in the   |       |
|                 | Unicode database                |       |
+-----------------+---------------------------------+-------+
| ``\uxxxx``      | Character with 16-bit hex value | \(4)  |
|                 | *xxxx*                          |       |
+-----------------+---------------------------------+-------+
| ``\Uxxxxxxxx``  | Character with 32-bit hex value | \(5)  |
|                 | *xxxxxxxx*                      |       |
+-----------------+---------------------------------+-------+
499 500 501 502

Notes:

(1)
503
   As in Standard C, up to three octal digits are accepted.
504 505

(2)
506
   Unlike in Standard C, exactly two hex digits are required.
507 508

(3)
509 510 511
   In a bytes literal, hexadecimal and octal escapes denote the byte with the
   given value. In a string literal, these escapes denote a Unicode character
   with the given value.
512 513

(4)
514
   Individual code units which form parts of a surrogate pair can be encoded using
515
   this escape sequence. Unlike in Standard C, exactly two hex digits are required.
516 517

(5)
518 519 520 521 522
   Any Unicode character can be encoded this way, but characters outside the Basic
   Multilingual Plane (BMP) will be encoded using a surrogate pair if Python is
   compiled to use 16-bit code units (the default).  Individual code units which
   form parts of a surrogate pair can be encoded using this escape sequence.

523

524
.. index:: unrecognized escape sequence
525 526 527 528 529

Unlike Standard C, all unrecognized escape sequences are left in the string
unchanged, i.e., *the backslash is left in the string*.  (This behavior is
useful when debugging: if an escape sequence is mistyped, the resulting output
is more easily recognized as broken.)  It is also important to note that the
530 531 532 533 534 535 536 537 538 539 540
escape sequences only recognized in string literals fall into the category of
unrecognized escapes for bytes literals.

Even in a raw string, string quotes can be escaped with a backslash, but the
backslash remains in the string; for example, ``r"\""`` is a valid string
literal consisting of two characters: a backslash and a double quote; ``r"\"``
is not a valid string literal (even a raw string cannot end in an odd number of
backslashes).  Specifically, *a raw string cannot end in a single backslash*
(since the backslash would escape the following quote character).  Note also
that a single backslash followed by a newline is interpreted as those two
characters as part of the string, *not* as a line continuation.
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


.. _string-catenation:

String literal concatenation
----------------------------

Multiple adjacent string literals (delimited by whitespace), possibly using
different quoting conventions, are allowed, and their meaning is the same as
their concatenation.  Thus, ``"hello" 'world'`` is equivalent to
``"helloworld"``.  This feature can be used to reduce the number of backslashes
needed, to split long strings conveniently across long lines, or even to add
comments to parts of strings, for example::

   re.compile("[A-Za-z_]"       # letter or underscore
              "[A-Za-z0-9_]*"   # letter, digit or underscore
             )

Note that this feature is defined at the syntactical level, but implemented at
compile time.  The '+' operator must be used to concatenate string expressions
at run time.  Also note that literal concatenation can use different quoting
styles for each component (even mixing raw strings and triple quoted strings).


.. _numbers:

Numeric literals
----------------

570 571
.. index:: number, numeric literal, integer literal
   floating point literal, hexadecimal literal
572
   octal literal, binary literal, decimal literal, imaginary literal, complex literal
573

574 575 576
There are three types of numeric literals: integers, floating point numbers, and
imaginary numbers.  There are no complex literals (complex numbers can be formed
by adding a real number and an imaginary number).
577 578 579 580 581 582 583 584 585 586 587 588 589 590

Note that numeric literals do not include a sign; a phrase like ``-1`` is
actually an expression composed of the unary operator '``-``' and the literal
``1``.


.. _integers:

Integer literals
----------------

Integer literals are described by the following lexical definitions:

.. productionlist::
591
   integer: `decimalinteger` | `octinteger` | `hexinteger` | `bininteger`
592
   decimalinteger: `nonzerodigit` `digit`* | "0"+
593 594
   nonzerodigit: "1"..."9"
   digit: "0"..."9"
595 596 597 598 599
   octinteger: "0" ("o" | "O") `octdigit`+
   hexinteger: "0" ("x" | "X") `hexdigit`+
   bininteger: "0" ("b" | "B") `bindigit`+
   octdigit: "0"..."7"
   hexdigit: `digit` | "a"..."f" | "A"..."F"
600
   bindigit: "0" | "1"
601

602 603
There is no limit for the length of integer literals apart from what can be
stored in available memory.
604 605 606 607 608 609 610 611 612

Note that leading zeros in a non-zero decimal number are not allowed. This is
for disambiguation with C-style octal literals, which Python used before version
3.0.

Some examples of integer literals::

   7     2147483647                        0o177    0b100110111
   3     79228162514264337593543950336     0o377    0x100000000
613
         79228162514264337593543950336              0xdeadbeef
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


.. _floating:

Floating point literals
-----------------------

Floating point literals are described by the following lexical definitions:

.. productionlist::
   floatnumber: `pointfloat` | `exponentfloat`
   pointfloat: [`intpart`] `fraction` | `intpart` "."
   exponentfloat: (`intpart` | `pointfloat`) `exponent`
   intpart: `digit`+
   fraction: "." `digit`+
   exponent: ("e" | "E") ["+" | "-"] `digit`+

Note that the integer and exponent parts are always interpreted using radix 10.
For example, ``077e010`` is legal, and denotes the same number as ``77e10``. The
allowed range of floating point literals is implementation-dependent. Some
examples of floating point literals::

   3.14    10.    .001    1e100    3.14e-10    0e0

Note that numeric literals do not include a sign; a phrase like ``-1`` is
actually an expression composed of the unary operator ``-`` and the literal
``1``.


.. _imaginary:

Imaginary literals
------------------

Imaginary literals are described by the following lexical definitions:

.. productionlist::
   imagnumber: (`floatnumber` | `intpart`) ("j" | "J")

An imaginary literal yields a complex number with a real part of 0.0.  Complex
numbers are represented as a pair of floating point numbers and have the same
restrictions on their range.  To create a complex number with a nonzero real
part, add a floating point number to it, e.g., ``(3+4j)``.  Some examples of
imaginary literals::

659
   3.14j   10.j    10j     .001j   1e100j  3.14e-10j
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


.. _operators:

Operators
=========

.. index:: single: operators

The following tokens are operators::

   +       -       *       **      /       //      %
   <<      >>      &       |       ^       ~
   <       >       <=      >=      ==      !=


.. _delimiters:

Delimiters
==========

.. index:: single: delimiters

The following tokens serve as delimiters in the grammar::

685 686
   (       )       [       ]       {       }
   ,       :       .       ;       @       =
687 688 689 690
   +=      -=      *=      /=      //=     %=
   &=      |=      ^=      >>=     <<=     **=

The period can also occur in floating-point and imaginary literals.  A sequence
691
of three periods has a special meaning as an ellipsis literal. The second half
692 693 694 695 696 697 698 699 700 701 702 703
of the list, the augmented assignment operators, serve lexically as delimiters,
but also perform an operation.

The following printing ASCII characters have special meaning as part of other
tokens or are otherwise significant to the lexical analyzer::

   '       "       #       \

The following printing ASCII characters are not used in Python.  Their
occurrence outside string literals and comments is an unconditional error::

   $       ?