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# 7.9. `unicodedata` — Unicode 数据库

This module provides access to the Unicode Character Database which defines character properties for all Unicode characters. The data in this database is based on the `UnicodeData.txt` file version 5.2.0 which is publicly available from ftp://ftp.unicode.org/.

The module uses the same names and symbols as defined by the UnicodeData File Format 5.2.0 (see https://www.unicode.org/reports/tr44/). It defines the following functions:

`unicodedata.``lookup`(name)

  Look up character by name. If a character with the given name is found, return the corresponding Unicode character. If not found, `KeyError` is raised.

`unicodedata.``name`(unichr[, default])

  Returns the name assigned to the Unicode character unichr as a string. If no name is defined, default is returned, or, if not given, `ValueError` is raised.

`unicodedata.``decimal`(unichr[, default])

  Returns the decimal value assigned to the Unicode character unichr as integer. If no such value is defined, default is returned, or, if not given, `ValueError` is raised.

`unicodedata.``digit`(unichr[, default])

  Returns the digit value assigned to the Unicode character unichr as integer. If no such value is defined, default is returned, or, if not given, `ValueError` is raised.

`unicodedata.``numeric`(unichr[, default])

  Returns the numeric value assigned to the Unicode character unichr as float. If no such value is defined, default is returned, or, if not given, `ValueError` is raised.

`unicodedata.``category`(unichr)

  Returns the general category assigned to the Unicode character unichr as string.

`unicodedata.``bidirectional`(unichr)

  Returns the bidirectional class assigned to the Unicode character unichr as string. If no such value is defined, an empty string is returned.

`unicodedata.``combining`(unichr)

  Returns the canonical combining class assigned to the Unicode character unichr as integer. Returns `0` if no combining class is defined.

`unicodedata.``east_asian_width`(unichr)

  Returns the east asian width assigned to the Unicode character unichr as string.

  2.4 新版功能.

`unicodedata.``mirrored`(unichr)

  Returns the mirrored property assigned to the Unicode character unichr as integer. Returns `1` if the character has been identified as a “mirrored” character in bidirectional text, `0` otherwise.

`unicodedata.``decomposition`(unichr)

  Returns the character decomposition mapping assigned to the Unicode character unichr as string. An empty string is returned in case no such mapping is defined.

`unicodedata.``normalize`(form, unistr)

  返回 Unicode 字符串 unistr 的正常形式 form 。 form 的有效值为 ‘NFC’ 、 ‘NFKC’ 、 ‘NFD’ 和 ‘NFKD’ 。

  Unicode 标准基于规范等价和兼容性等效的定义定义了 Unicode 字符串的各种规范化形式。在 Unicode 中，可以以各种方式表示多个字符。 例如，字符 U+00C7 （带有 CEDILLA 的 LATIN CAPITAL LETTER C ）也可以表示为序列 U+0043（ LATIN CAPITAL LETTER C ）U+0327（ COMBINING CEDILLA ）。

  对于每个字符，有两种正规形式：正规形式 C 和正规形式 D 。正规形式D（NFD）也称为规范分解，并将每个字符转换为其分解形式。 正规形式C（NFC）首先应用规范分解，然后再次组合预组合字符。

  除了这两种形式之外，还有两种基于兼容性等效的其他常规形式。 在 Unicode 中，支持某些字符，这些字符通常与其他字符统一。 例如， U+2160（ROMAN NUMERAL ONE）与 U+0049（LATIN CAPITAL LETTER I）完全相同。 但是， Unicode 支持它与现有字符集（例如 gb2312 ）的兼容性。

  正规形式KD（NFKD）将应用兼容性分解，即用其等价项替换所有兼容性字符。 正规形式KC（NFKC）首先应用兼容性分解，然后是规范组合。

  即使两个 unicode 字符串被规范化并且人类读者看起来相同，如果一个具有组合字符而另一个没有，则它们可能无法相等。

  2.3 新版功能.

此外，该模块暴露了以下常量：

`unicodedata.``unidata_version`

  此模块中使用的 Unicode 数据库的版本。

  2.3 新版功能.

`unicodedata.``ucd_3_2_0`

  这是一个与整个模块具有相同方法的对象，但对于需要此特定版本的 Unicode 数据库（如 IDNA ）的应用程序，则使用 Unicode 数据库版本 3.2 。

  2.5 新版功能.

示例：

    >>> import unicodedata
    >>> unicodedata.lookup('LEFT CURLY BRACKET')
    u'{'
    >>> unicodedata.name(u'/')
    'SOLIDUS'
    >>> unicodedata.decimal(u'9')
    9
    >>> unicodedata.decimal(u'a')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: not a decimal
    >>> unicodedata.category(u'A')  # 'L'etter, 'u'ppercase
    'Lu'
    >>> unicodedata.bidirectional(u'\u0660') # 'A'rabic, 'N'umber
    'AN'