QTextCodec露

PyQt5.QtCore.QTextCodec

Description露

The QTextCodec class provides conversions between text encodings.

Qt uses Unicode to store, draw and manipulate strings. In many situations you may wish to deal with data that uses a different encoding. For example, most Japanese documents are still stored in Shift-JIS or ISO 2022-JP, while Russian users often have their documents in KOI8-R or Windows-1251.

Qt provides a set of QTextCodec classes to help with converting non-Unicode formats to and from Unicode. You can also create your own codec classes.

The supported encodings are:

  • Big5

  • Big5-HKSCS

  • CP949

  • EUC-JP

  • EUC-KR

  • GB18030

  • HP-ROMAN8

  • IBM 850

  • IBM 866

  • IBM 874

  • ISO 2022-JP

  • ISO 8859-1 to 10

  • ISO 8859-13 to 16

  • Iscii-Bng, Dev, Gjr, Knd, Mlm, Ori, Pnj, Tlg, and Tml

  • KOI8-R

  • KOI8-U

  • Macintosh

  • Shift-JIS

  • TIS-620

  • TSCII

  • UTF-8

  • UTF-16

  • UTF-16BE

  • UTF-16LE

  • UTF-32

  • UTF-32BE

  • UTF-32LE

  • Windows-1250 to 1258

If Qt is compiled with ICU support enabled, most codecs supported by ICU will also be available to the application.

QTextCodecs can be used as follows to convert some locally encoded string to Unicode. Suppose you have some string encoded in Russian KOI8-R encoding, and want to convert it to Unicode. The simple way to do it is like this:

# QByteArray encodedString = "...";
# QTextCodec *codec = QTextCodec::codecForName("KOI8-R");
# QString string = codec->toUnicode(encodedString);

After this, string holds the text converted to Unicode. Converting a string from Unicode to the local encoding is just as easy:

# QString string = "...";
# QTextCodec *codec = QTextCodec::codecForName("KOI8-R");
# QByteArray encodedString = codec->fromUnicode(string);

To read or write files in various encodings, use QTextStream and its setCodec() function. See the Codecs example for an application of QTextCodec to file I/O.

Some care must be taken when trying to convert the data in chunks, for example, when receiving it over a network. In such cases it is possible that a multi-byte character will be split over two chunks. At best this might result in the loss of a character and at worst cause the entire conversion to fail.

The approach to use in these situations is to create a QTextDecoder object for the codec and use this QTextDecoder for the whole decoding process, as shown below:

# QTextCodec *codec = QTextCodec::codecForName("Shift-JIS");
# QTextDecoder *decoder = codec->makeDecoder();

# QString string;
# while (new_data_available()) {
#     QByteArray chunk = get_new_data();
#     string += decoder->toUnicode(chunk);
# }
# delete decoder;

The QTextDecoder object maintains state between chunks and therefore works correctly even if a multi-byte character is split between chunks.

Creating Your Own Codec Class露

Support for new text encodings can be added to Qt by creating QTextCodec subclasses.

The pure virtual functions describe the encoder to the system and the coder is used as required in the different text file formats supported by QTextStream, and under X11, for the locale-specific character input and output.

To add support for another encoding to Qt, make a subclass of QTextCodec and implement the functions listed in the table below.

Function

Description

name()

Returns the official name for the encoding. If the encoding is listed in the IANA character-sets encoding file, the name should be the preferred MIME name for the encoding.

aliases()

Returns a list of alternative names for the encoding. QTextCodec provides a default implementation that returns an empty list. For example, 鈥淚SO-8859-1鈥 has 鈥渓atin1鈥, 鈥淐P819鈥, 鈥淚BM819鈥, and 鈥渋so-ir-100鈥 as aliases.

mibEnum()

Return the MIB enum for the encoding if it is listed in the IANA character-sets encoding file.

convertToUnicode()

Converts an 8-bit character string to Unicode.

convertFromUnicode()

Converts a Unicode string to an 8-bit character string.

See also

QTextStream, QTextDecoder, QTextEncoder, Text Codecs Example.

Enums露

ConversionFlag

Member

Value

Description
ConvertInvalidToNull

0x80000000

If this flag is set, each invalid input character is output as a null character.
DefaultConversion

0

No flag is set.
IgnoreHeader

0x1

Ignore any Unicode byte-order mark and don鈥檛 generate any.

Methods露

__init__()

Constructs a QTextCodec, and gives it the highest precedence. The QTextCodec should always be constructed on the heap (i.e. with new). Qt takes ownership and will delete it when the application terminates.

aliases() → List[QByteArray]

Subclasses can return a number of aliases for the codec in question.

Standard aliases for codecs can be found in the IANA character-sets encoding file.

@staticmethod
availableCodecs() → List[QByteArray]

Returns the list of all available codecs, by name. Call codecForName() to obtain the QTextCodec for the name.

The list may contain many mentions of the same codec if the codec has aliases.

See also

availableMibs(), name(), aliases().

@staticmethod
availableMibs() → List[int]

Returns the list of MIBs for all available codecs. Call codecForMib() to obtain the QTextCodec for the MIB.

See also

availableCodecs(), mibEnum().

canEncode(str) → bool

This is an overloaded function.

s contains the string being tested for encode-ability.

@staticmethod
codecForHtml(Union[QByteArray, bytes, bytearray]) → QTextCodec

This is an overloaded function.

Tries to detect the encoding of the provided snippet of HTML in the given byte array, ba, by checking the BOM (Byte Order Mark) and the content-type meta header and returns a QTextCodec instance that is capable of decoding the html to unicode. If the codec cannot be detected, this overload returns a Latin-1 QTextCodec.

@staticmethod
codecForHtml(Union[QByteArray, bytes, bytearray], QTextCodec) → QTextCodec

Tries to detect the encoding of the provided snippet of HTML in the given byte array, ba, by checking the BOM (Byte Order Mark) and the content-type meta header and returns a QTextCodec instance that is capable of decoding the html to unicode. If the codec cannot be detected from the content provided, defaultCodec is returned.

See also

codecForUtfText().

@staticmethod
codecForLocale() → QTextCodec

Returns a pointer to the codec most suitable for this locale.

On Windows, the codec will be based on a system locale. On Unix systems, the codec will might fall back to using the iconv library if no builtin codec for the locale can be found.

Note that in these cases the codec鈥檚 name will be 鈥淪ystem鈥.

See also

setCodecForLocale().

@staticmethod
codecForMib(int) → QTextCodec

Returns the QTextCodec which matches the mibEnum() mib.

@staticmethod
codecForName(Union[QByteArray, bytes, bytearray]) → QTextCodec

Searches all installed QTextCodec objects and returns the one which best matches name; the match is case-insensitive. Returns 0 if no codec matching the name name could be found.

@staticmethod
codecForName(str) → QTextCodec

TODO

@staticmethod
codecForUtfText(Union[QByteArray, bytes, bytearray]) → QTextCodec

This is an overloaded function.

Tries to detect the encoding of the provided snippet ba by using the BOM (Byte Order Mark) and returns a QTextCodec instance that is capable of decoding the text to unicode. If the codec cannot be detected, this overload returns a Latin-1 QTextCodec.

See also

codecForHtml().

@staticmethod
codecForUtfText(Union[QByteArray, bytes, bytearray], QTextCodec) → QTextCodec

Tries to detect the encoding of the provided snippet ba by using the BOM (Byte Order Mark) and returns a QTextCodec instance that is capable of decoding the text to unicode. If the codec cannot be detected from the content provided, defaultCodec is returned.

See also

codecForHtml().

convertToUnicode(bytes, ConverterState) → str

TODO

fromUnicode(str) → QByteArray

Converts str from Unicode to the encoding of this codec, and returns the result in a QByteArray.

makeDecoder(flags: Union[ConversionFlags, ConversionFlag] = DefaultConversion) → QTextDecoder

Creates a QTextDecoder with a specified flags to decode chunks of char \* data to create chunks of Unicode data.

The caller is responsible for deleting the returned object.

makeEncoder(flags: Union[ConversionFlags, ConversionFlag] = DefaultConversion) → QTextEncoder

Creates a QTextEncoder with a specified flags to encode chunks of Unicode data as char \* data.

The caller is responsible for deleting the returned object.

mibEnum() → int

TODO

name() → QByteArray

TODO

@staticmethod
setCodecForLocale(QTextCodec)

Set the codec to c; this will be returned by codecForLocale(). If c is a null pointer, the codec is reset to the default.

This might be needed for some applications that want to use their own mechanism for setting the locale.

See also

codecForLocale().

toUnicode(Union[QByteArray, bytes, bytearray]) → str

Converts a from the encoding of this codec to Unicode, and returns the result in a QString.

toUnicode(str) → str

This is an overloaded function.

chars contains the source characters.

toUnicode(bytes, state: ConverterState = None) → str

TODO