QTextCodec

The QTextCodec class provides conversions between text encodings. More

Inheritance diagram of PySide2.QtCore.QTextCodec

Synopsis

Functions

Virtual functions

Static functions

Detailed Description

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.

QTextCodec s 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:

encodedString = QByteArray("...")
codec = QTextCodec.codecForName("KOI8-R")
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:

string = u"..."
codec = QTextCodec.codecForName("KOI8-R")
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:

codec = QTextCodec.codecForName("Shift-JIS")
decoder = codec.makeDecoder()

string = u''
while new_data_available():
    chunk = get_new_data()
    string += decoder.toUnicode(chunk)

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

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, “ISO-8859-1” has “latin1”, “CP819”, “IBM819”, and “iso-ir-100” 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

class QTextCodec

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.

PySide2.QtCore.QTextCodec.ConversionFlag

Constant

Description

QTextCodec.DefaultConversion

No flag is set.

QTextCodec.ConvertInvalidToNull

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

QTextCodec.IgnoreHeader

Ignore any Unicode byte-order mark and don’t generate any.

PySide2.QtCore.QTextCodec.aliases()
Return type

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 .

static PySide2.QtCore.QTextCodec.availableCodecs()
Return type

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.

static PySide2.QtCore.QTextCodec.availableMibs()
Return type

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

PySide2.QtCore.QTextCodec.canEncode(arg__1)
Parameters

arg__1QChar

Return type

bool

Returns true if the Unicode character ch can be fully encoded with this codec; otherwise returns false .

PySide2.QtCore.QTextCodec.canEncode(arg__1)
Parameters

arg__1 – unicode

Return type

bool

static PySide2.QtCore.QTextCodec.codecForHtml(ba)
Parameters

baQByteArray

Return type

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 .

static PySide2.QtCore.QTextCodec.codecForHtml(ba, defaultCodec)
Parameters
Return type

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.

static PySide2.QtCore.QTextCodec.codecForLocale()
Return type

QTextCodec

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

The codec will be retrieved from ICU where that backend is in use, otherwise it may be obtained from an OS-specific API. In the latter case, the codec’s name may be “System”.

static PySide2.QtCore.QTextCodec.codecForMib(mib)
Parameters

mibint

Return type

QTextCodec

Returns the QTextCodec which matches the MIBenum mib .

static PySide2.QtCore.QTextCodec.codecForName(name)
Parameters

nameQByteArray

Return type

QTextCodec

static PySide2.QtCore.QTextCodec.codecForName(name)
Parameters

name – str

Return type

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.

static PySide2.QtCore.QTextCodec.codecForUtfText(ba, defaultCodec)
Parameters
Return type

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. This function can detect one of the following codecs:

  • UTF-32 Little Endian

  • UTF-32 Big Endian

  • UTF-16 Little Endian

  • UTF-16 Big Endian

  • UTF-8

If the codec cannot be detected from the content provided, defaultCodec is returned.

See also

codecForHtml()

static PySide2.QtCore.QTextCodec.codecForUtfText(ba)
Parameters

baQByteArray

Return type

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. This function can detect one of the following codecs:

  • UTF-32 Little Endian

  • UTF-32 Big Endian

  • UTF-16 Little Endian

  • UTF-16 Big Endian

  • UTF-8

If the codec cannot be detected from the content provided, this overload returns a Latin-1 QTextCodec .

See also

codecForHtml()

PySide2.QtCore.QTextCodec.convertToUnicode(in, length, state)
Parameters
Return type

unicode

QTextCodec subclasses must reimplement this function.

Converts the first len characters of chars from the encoding of the subclass to Unicode, and returns the result in a QString .

state can be None , in which case the conversion is stateless and default conversion rules should be used. If state is not 0, the codec should save the state after the conversion in state , and adjust the remainingChars and invalidChars members of the struct.

PySide2.QtCore.QTextCodec.fromUnicode(uc)
Parameters

uc – unicode

Return type

QByteArray

PySide2.QtCore.QTextCodec.makeDecoder([flags=QTextCodec.DefaultConversion])
Parameters

flagsConversionFlags

Return type

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.

PySide2.QtCore.QTextCodec.makeEncoder([flags=QTextCodec.DefaultConversion])
Parameters

flagsConversionFlags

Return type

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.

PySide2.QtCore.QTextCodec.mibEnum()
Return type

int

Subclasses of QTextCodec must reimplement this function. It returns the MIBenum (see IANA character-sets encoding file for more information). It is important that each QTextCodec subclass returns the correct unique value for this function.

PySide2.QtCore.QTextCodec.name()
Return type

QByteArray

QTextCodec subclasses must reimplement this function. It returns the name of the encoding supported by the subclass.

If the codec is registered as a character set in the IANA character-sets encoding file this method should return the preferred mime name for the codec if defined, otherwise its name.

static PySide2.QtCore.QTextCodec.setCodecForLocale(c)
Parameters

cQTextCodec

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()

PySide2.QtCore.QTextCodec.toUnicode(arg__1)
Parameters

arg__1QByteArray

Return type

unicode

PySide2.QtCore.QTextCodec.toUnicode(chars)
Parameters

chars – str

Return type

unicode

This is an overloaded function.

chars contains the source characters.

PySide2.QtCore.QTextCodec.toUnicode(in, length[, state=None])
Parameters
Return type

unicode

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

The state of the convertor used is updated.