diff options
Diffstat (limited to 'Doc/reference/lexical_analysis.rst')
| -rw-r--r-- | Doc/reference/lexical_analysis.rst | 41 |
1 files changed, 31 insertions, 10 deletions
diff --git a/Doc/reference/lexical_analysis.rst b/Doc/reference/lexical_analysis.rst index 4b49738e26..94f219b023 100644 --- a/Doc/reference/lexical_analysis.rst +++ b/Doc/reference/lexical_analysis.rst @@ -401,7 +401,7 @@ String literals are described by the following lexical definitions: .. productionlist:: stringliteral: [`stringprefix`](`shortstring` | `longstring`) - stringprefix: "r" | "R" + stringprefix: "r" | "u" | "R" | "U" shortstring: "'" `shortstringitem`* "'" | '"' `shortstringitem`* '"' longstring: "'''" `longstringitem`* "'''" | '"""' `longstringitem`* '"""' shortstringitem: `shortstringchar` | `stringescapeseq` @@ -412,7 +412,7 @@ String literals are described by the following lexical definitions: .. productionlist:: bytesliteral: `bytesprefix`(`shortbytes` | `longbytes`) - bytesprefix: "b" | "B" | "br" | "Br" | "bR" | "BR" + bytesprefix: "b" | "B" | "br" | "Br" | "bR" | "BR" | "rb" | "rB" | "Rb" | "RB" shortbytes: "'" `shortbytesitem`* "'" | '"' `shortbytesitem`* '"' longbytes: "'''" `longbytesitem`* "'''" | '"""' `longbytesitem`* '"""' shortbytesitem: `shortbyteschar` | `bytesescapeseq` @@ -441,10 +441,24 @@ 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. +As of Python 3.3 it is possible again to prefix unicode strings with a +``u`` prefix to simplify maintenance of dual 2.x and 3.x codebases. + Both string and bytes literals may optionally be prefixed with a letter ``'r'`` or ``'R'``; such strings are called :dfn:`raw strings` and treat backslashes as literal characters. As a result, in string literals, ``'\U'`` and ``'\u'`` -escapes in raw strings are not treated specially. +escapes in raw strings are not treated specially. Given that Python 2.x's raw +unicode literals behave differently than Python 3.x's the ``'ur'`` syntax +is not supported. + + .. versionadded:: 3.3 + The ``'rb'`` prefix of raw bytes literals has been added as a synonym + of ``'br'``. + + .. versionadded:: 3.3 + Support for the unicode legacy literal (``u'value'``) was reintroduced + to simplify the maintenance of dual Python 2.x and 3.x codebases. + See :pep:`414` for more information. 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 @@ -492,13 +506,13 @@ Escape sequences only recognized in string literals are: +-----------------+---------------------------------+-------+ | Escape Sequence | Meaning | Notes | +=================+=================================+=======+ -| ``\N{name}`` | Character named *name* in the | | +| ``\N{name}`` | Character named *name* in the | \(4) | | | Unicode database | | +-----------------+---------------------------------+-------+ -| ``\uxxxx`` | Character with 16-bit hex value | \(4) | +| ``\uxxxx`` | Character with 16-bit hex value | \(5) | | | *xxxx* | | +-----------------+---------------------------------+-------+ -| ``\Uxxxxxxxx`` | Character with 32-bit hex value | \(5) | +| ``\Uxxxxxxxx`` | Character with 32-bit hex value | \(6) | | | *xxxxxxxx* | | +-----------------+---------------------------------+-------+ @@ -516,13 +530,15 @@ Notes: with the given value. (4) + .. versionchanged:: 3.3 + Support for name aliases [#]_ has been added. + +(5) Individual code units which form parts of a surrogate pair can be encoded using this escape sequence. Exactly four hex digits are required. -(5) - 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). Exactly eight hex digits +(6) + Any Unicode character can be encoded this way. Exactly eight hex digits are required. @@ -706,3 +722,8 @@ The following printing ASCII characters are not used in Python. Their occurrence outside string literals and comments is an unconditional error:: $ ? ` + + +.. rubric:: Footnotes + +.. [#] http://www.unicode.org/Public/6.1.0/ucd/NameAliases.txt |