class QTextStream

The QTextStream class provides a convenient interface for reading and writing text. More…

Inheritance diagram of PySide6.QtCore.QTextStream

Synopsis

Methods

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

QTextStream can operate on a QIODevice , a QByteArray or a QString . Using QTextStream ‘s streaming operators, you can conveniently read and write words, lines and numbers. For generating text, QTextStream supports formatting options for field padding and alignment, and formatting of numbers. Example:

data = QFile("output.txt")
if data.open(QFile.WriteOnly | QFile.Truncate):
    out = QTextStream(data)
    out << "Result: " << qSetFieldWidth(10) << left << 3.14 << 2.7
    # writes "Result: 3.14      2.7       "

It’s also common to use QTextStream to read console input and write console output. QTextStream is locale aware, and will automatically decode standard input using the correct encoding. Example:

stream = QTextStream(stdin)
line = QString()
while stream.readLineInto(line):
    ...

Besides using QTextStream ‘s constructors, you can also set the device or string QTextStream operates on by calling setDevice() or setString() . You can seek to a position by calling seek() , and atEnd() will return true when there is no data left to be read. If you call flush() , QTextStream will empty all data from its write buffer into the device and call flush() on the device.

Internally, QTextStream uses a Unicode based buffer, and QStringConverter is used by QTextStream to automatically support different encodings. By default, UTF-8 is used for reading and writing, but you can also set the encoding by calling setEncoding() . Automatic Unicode detection is also supported. When this feature is enabled (the default behavior), QTextStream will detect the UTF-8, UTF-16 or the UTF-32 BOM (Byte Order Mark) and switch to the appropriate UTF encoding when reading. QTextStream does not write a BOM by default, but you can enable this by calling setGenerateByteOrderMark (true). When QTextStream operates on a QString directly, the encoding is disabled.

There are three general ways to use QTextStream when reading text files:

  • Chunk by chunk, by calling readLine() or readAll() .

  • Word by word. QTextStream supports streaming into QString s, QByteArray s and char* buffers. Words are delimited by space, and leading white space is automatically skipped.

  • Character by character, by streaming into QChar or char types. This method is often used for convenient input handling when parsing files, independent of character encoding and end-of-line semantics. To skip white space, call skipWhiteSpace() .

Since the text stream uses a buffer, you should not read from the stream using the implementation of a superclass. For instance, if you have a QFile and read from it directly using readLine() instead of using the stream, the text stream’s internal position will be out of sync with the file’s position.

By default, when reading numbers from a stream of text, QTextStream will automatically detect the number’s base representation. For example, if the number starts with “0x”, it is assumed to be in hexadecimal form. If it starts with the digits 1-9, it is assumed to be in decimal form, and so on. You can set the integer base, thereby disabling the automatic detection, by calling setIntegerBase() . Example:

in = QTextStream("0x50 0x20")
firstNumber, = int()
in >> firstNumber # firstNumber == 80
in >> dec >> secondNumber # secondNumber == 0
ch = char()
in >> ch # ch == 'x'

QTextStream supports many formatting options for generating text. You can set the field width and pad character by calling setFieldWidth() and setPadChar() . Use setFieldAlignment() to set the alignment within each field. For real numbers, call setRealNumberNotation() and setRealNumberPrecision() to set the notation ( SmartNotation , ScientificNotation , FixedNotation ) and precision in digits of the generated number. Some extra number formatting options are also available through setNumberFlags() .

Like <iostream> in the standard C++ library, QTextStream also defines several global manipulator functions:

Manipulator

Description

bin

Same as setIntegerBase (2).

oct

Same as setIntegerBase (8).

dec

Same as setIntegerBase (10).

hex

Same as setIntegerBase (16).

showbase

Same as setNumberFlags ( numberFlags() | ShowBase ).

forcesign

Same as setNumberFlags ( numberFlags() | ForceSign ).

forcepoint

Same as setNumberFlags ( numberFlags() | ForcePoint ).

noshowbase

Same as setNumberFlags ( numberFlags() & ~ ShowBase ).

noforcesign

Same as setNumberFlags ( numberFlags() & ~ ForceSign ).

noforcepoint

Same as setNumberFlags ( numberFlags() & ~ ForcePoint ).

uppercasebase

Same as setNumberFlags ( numberFlags() | UppercaseBase ).

uppercasedigits

Same as setNumberFlags ( numberFlags() | UppercaseDigits ).

lowercasebase

Same as setNumberFlags ( numberFlags() & ~ UppercaseBase ).

lowercasedigits

Same as setNumberFlags ( numberFlags() & ~ UppercaseDigits ).

fixed

Same as setRealNumberNotation ( FixedNotation ).

scientific

Same as setRealNumberNotation ( ScientificNotation ).

left

Same as setFieldAlignment ( AlignLeft ).

right

Same as setFieldAlignment ( AlignRight ).

center

Same as setFieldAlignment ( AlignCenter ).

endl

Same as operator<<(’\n’) and flush() .

flush

Same as flush() .

reset

Same as reset() .

ws

Same as skipWhiteSpace() .

bom

Same as setGenerateByteOrderMark (true).

In addition, Qt provides three global manipulators that take a parameter: qSetFieldWidth() , qSetPadChar() , and qSetRealNumberPrecision() .

class RealNumberNotation

This enum specifies which notations to use for expressing float and double as strings.

Constant

Description

QTextStream.ScientificNotation

Scientific notation (printf()'s %e flag).

QTextStream.FixedNotation

Fixed-point notation (printf()'s %f flag).

QTextStream.SmartNotation

Scientific or fixed-point notation, depending on which makes most sense (printf()'s %g flag).

See also

setRealNumberNotation()

class FieldAlignment

This enum specifies how to align text in fields when the field is wider than the text that occupies it.

Constant

Description

QTextStream.AlignLeft

Pad on the right side of fields.

QTextStream.AlignRight

Pad on the left side of fields.

QTextStream.AlignCenter

Pad on both sides of field.

QTextStream.AlignAccountingStyle

Same as AlignRight, except that the sign of a number is flush left.

See also

setFieldAlignment()

class Status

This enum describes the current status of the text stream.

Constant

Description

QTextStream.Ok

The text stream is operating normally.

QTextStream.ReadPastEnd

The text stream has read past the end of the data in the underlying device.

QTextStream.ReadCorruptData

The text stream has read corrupt data.

QTextStream.WriteFailed

The text stream cannot write to the underlying device.

See also

status()

class NumberFlag

(inherits enum.Flag) This enum specifies various flags that can be set to affect the output of integers, floats, and doubles.

Constant

Description

QTextStream.ShowBase

Show the base as a prefix if the base is 16 (“0x”), 8 (“0”), or 2 (“0b”).

QTextStream.ForcePoint

Always put the decimal separator in numbers, even if there are no decimals.

QTextStream.ForceSign

Always put the sign in numbers, even for positive numbers.

QTextStream.UppercaseBase

Use uppercase versions of base prefixes (“0X”, “0B”).

QTextStream.UppercaseDigits

Use uppercase letters for expressing digits 10 to 35 instead of lowercase.

See also

setNumberFlags()

__init__()

Constructs a QTextStream . Before you can use it for reading or writing, you must assign a device or a string.

See also

setDevice() setString()

__init__(device)
Parameters:

device – QIODevice

Constructs a QTextStream that operates on device.

__init__(array[, openMode=QIODeviceBase.OpenModeFlag.ReadWrite])
Parameters:

Constructs a QTextStream that operates on array, using openMode to define the open mode. Internally, the array is wrapped by a QBuffer .

atEnd()
Return type:

bool

Returns true if there is no more data to be read from the QTextStream ; otherwise returns false. This is similar to, but not the same as calling atEnd() , as QTextStream also takes into account its internal Unicode buffer.

autoDetectUnicode()
Return type:

bool

Returns true if automatic Unicode detection is enabled, otherwise returns false. Automatic Unicode detection is enabled by default.

device()
Return type:

QIODevice

Returns the current device associated with the QTextStream , or None if no device has been assigned.

encoding()
Return type:

Encoding

Returns the encoding that is current assigned to the stream.

fieldAlignment()
Return type:

FieldAlignment

Returns the current field alignment.

fieldWidth()
Return type:

int

Returns the current field width.

See also

setFieldWidth()

flush()

Flushes any buffered data waiting to be written to the device.

If QTextStream operates on a string, this function does nothing.

generateByteOrderMark()
Return type:

bool

Returns true if QTextStream is set to generate the UTF BOM (Byte Order Mark) when using a UTF encoding; otherwise returns false. UTF BOM generation is set to false by default.

integerBase()
Return type:

int

Returns the current base of integers. 0 means that the base is detected when reading, or 10 (decimal) when generating numbers.

See also

setIntegerBase() number() numberFlags()

locale()
Return type:

QLocale

Returns the locale for this stream. The default locale is C.

See also

setLocale()

numberFlags()
Return type:

Combination of NumberFlag

Returns the current number flags.

__lshift__(ch)
Parameters:

ch – QChar

Return type:

QTextStream

Writes the character c to the stream, then returns a reference to the QTextStream .

See also

setFieldWidth()

__lshift__(s)
Parameters:

s – QLatin1String

Return type:

QTextStream

__lshift__(s)
Parameters:

s – str

Return type:

QTextStream

This is an overloaded function.

Writes string to the stream, and returns a reference to the QTextStream .

__lshift__(m)
Parameters:

m – QTextStreamManipulator

Return type:

QTextStream

__lshift__(ch)
Parameters:

ch – int

Return type:

QTextStream

This is an overloaded function.

Converts c from ASCII to a QChar , then writes it to the stream.

__lshift__(array)
Parameters:

array – QByteArray

Return type:

QTextStream

This is an overloaded function.

Writes array to the stream. The contents of array are converted with fromUtf8() .

__lshift__(node)
Parameters:

node – QDomNode

Return type:

QTextStream

__lshift__(s)
Parameters:

s – str

Return type:

QTextStream

Writes the string string to the stream, and returns a reference to the QTextStream . The string is first encoded using the assigned encoding (the default is UTF-8) before it is written to the stream.

__lshift__(f)
Parameters:

f – float

Return type:

QTextStream

This is an overloaded function.

Writes the double f to the stream.

__lshift__(i)
Parameters:

i – int

Return type:

QTextStream

This is an overloaded function.

Writes the signed long i to the stream.

__lshift__(i)
Parameters:

i – int

Return type:

QTextStream

This is an overloaded function.

Writes the unsigned long i to the stream.

__rshift__(array)
Parameters:

array – QByteArray

Return type:

QTextStream

This is an overloaded function.

Converts the word to UTF-8, then stores it in array.

See also

toLatin1()

padChar()
Return type:

QChar

Returns the current pad character.

pos()
Return type:

int

Returns the device position corresponding to the current position of the stream, or -1 if an error occurs (e.g., if there is no device or string, or if there’s a device error).

Because QTextStream is buffered, this function may have to seek the device to reconstruct a valid device position. This operation can be expensive, so you may want to avoid calling this function in a tight loop.

See also

seek()

read(maxlen)
Parameters:

maxlen – int

Return type:

str

Reads at most maxlen characters from the stream, and returns the data read as a QString .

readAll()
Return type:

str

Reads the entire content of the stream, and returns it as a QString . Avoid this function when working on large files, as it will consume a significant amount of memory.

Calling readLine() is better if you do not know how much data is available.

See also

readLine()

readLine([maxlen=0])
Parameters:

maxlen – int

Return type:

str

Reads one line of text from the stream, and returns it as a QString . The maximum allowed line length is set to maxlen. If the stream contains lines longer than this, then the lines will be split after maxlen characters and returned in parts.

If maxlen is 0, the lines can be of any length.

The returned line has no trailing end-of-line characters (”\n” or “\r\n”), so calling trimmed() can be unnecessary.

If the stream has read to the end of the file, readLine() will return a null QString . For strings, or for devices that support it, you can explicitly test for the end of the stream using atEnd() .

readLineInto(line[, maxlen=0])
Parameters:

  • line – str

  • maxlen – int

Return type:

bool

Reads one line of text from the stream into line. If line is None, the read line is not stored.

The maximum allowed line length is set to maxlen. If the stream contains lines longer than this, then the lines will be split after maxlen characters and returned in parts.

If maxlen is 0, the lines can be of any length.

The resulting line has no trailing end-of-line characters (”\n” or “\r\n”), so calling trimmed() can be unnecessary.

If line has sufficient capacity for the data that is about to be read, this function may not need to allocate new memory. Because of this, it can be faster than readLine() .

Returns false if the stream has read to the end of the file or an error has occurred; otherwise returns true. The contents in line before the call are discarded in any case.

realNumberNotation()
Return type:

RealNumberNotation

Returns the current real number notation.

realNumberPrecision()
Return type:

int

Returns the current real number precision, or the number of fraction digits QTextStream will write when generating real numbers ( FixedNotation , ScientificNotation ), or the maximum number of significant digits ( SmartNotation ).

reset()

Resets QTextStream ‘s formatting options, bringing it back to its original constructed state. The device, string and any buffered data is left untouched.

resetStatus()

Resets the status of the text stream.

seek(pos)
Parameters:

pos – int

Return type:

bool

Seeks to the position pos in the device. Returns true on success; otherwise returns false.

setAutoDetectUnicode(enabled)
Parameters:

enabled – bool

If enabled is true, QTextStream will attempt to detect Unicode encoding by peeking into the stream data to see if it can find the UTF-8, UTF-16, or UTF-32 Byte Order Mark (BOM). If this mark is found, QTextStream will replace the current encoding with the UTF encoding.

This function can be used together with setEncoding() . It is common to set the encoding to UTF-8, and then enable UTF-16 detection.

setDevice(device)
Parameters:

device – QIODevice

Sets the current device to device. If a device has already been assigned, QTextStream will call flush() before the old device is replaced.

Note

This function resets locale to the default locale (‘C’) and encoding to the default encoding, UTF-8.

See also

device() setString()

setEncoding(encoding)
Parameters:

encoding – Encoding

Sets the encoding for this stream to encoding. The encoding is used for decoding any data that is read from the assigned device, and for encoding any data that is written. By default, Utf8 is used, and automatic unicode detection is enabled.

If QTextStream operates on a string, this function does nothing.

Warning

If you call this function while the text stream is reading from an open sequential socket, the internal buffer may still contain text decoded using the old encoding.

See also

encoding() setAutoDetectUnicode() setLocale()

setFieldAlignment(alignment)
Parameters:

alignment – FieldAlignment

Sets the field alignment to mode. When used together with setFieldWidth() , this function allows you to generate formatted output with text aligned to the left, to the right or center aligned.

setFieldWidth(width)
Parameters:

width – int

Sets the current field width to width. If width is 0 (the default), the field width is equal to the length of the generated text.

Note

The field width applies to every element appended to this stream after this function has been called (e.g., it also pads endl). This behavior is different from similar classes in the STL, where the field width only applies to the next element.

See also

fieldWidth() setPadChar()

setGenerateByteOrderMark(generate)
Parameters:

generate – bool

If generate is true and a UTF encoding is used, QTextStream will insert the BOM (Byte Order Mark) before any data has been written to the device. If generate is false, no BOM will be inserted. This function must be called before any data is written. Otherwise, it does nothing.

See also

generateByteOrderMark() bom()

setIntegerBase(base)
Parameters:

base – int

Sets the base of integers to base, both for reading and for generating numbers. base can be either 2 (binary), 8 (octal), 10 (decimal) or 16 (hexadecimal). If base is 0, QTextStream will attempt to detect the base by inspecting the data on the stream. When generating numbers, QTextStream assumes base is 10 unless the base has been set explicitly.

See also

integerBase() number() setNumberFlags()

setLocale(locale)
Parameters:

locale – QLocale

Sets the locale for this stream to locale. The specified locale is used for conversions between numbers and their string representations.

The default locale is C and it is a special case - the thousands group separator is not used for backward compatibility reasons.

See also

locale()

setNumberFlags(flags)
Parameters:

flags – Combination of NumberFlag

Sets the current number flags to flags. flags is a set of flags from the NumberFlag enum, and describes options for formatting generated code (e.g., whether or not to always write the base or sign of a number).

setPadChar(ch)
Parameters:

ch – QChar

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

Sets the pad character to ch. The default value is the ASCII space character (’ ‘), or QChar (0x20). This character is used to fill in the space in fields when generating text.

Example:

s = QString()
out = QTextStream(s)
out.setFieldWidth(10)
out.setFieldAlignment(QTextStream.AlignCenter)
out.setPadChar('-')
out << "Qt" << "rocks!"

The string s contains:

Qtrocksnot -= 1

See also

padChar() setFieldWidth()

setRealNumberNotation(notation)
Parameters:

notation – RealNumberNotation

Sets the real number notation to notation ( SmartNotation , FixedNotation , ScientificNotation ). When reading and generating numbers, QTextStream uses this value to detect the formatting of real numbers.

setRealNumberPrecision(precision)
Parameters:

precision – int

Sets the precision of real numbers to precision. This value describes the number of fraction digits QTextStream should write when generating real numbers ( FixedNotation , ScientificNotation ), or the maximum number of significant digits ( SmartNotation ).

The precision cannot be a negative value. The default value is 6.

setStatus(status)
Parameters:

status – Status

Sets the status of the text stream to the status given.

Subsequent calls to setStatus() are ignored until resetStatus() is called.

skipWhiteSpace()

Reads and discards whitespace from the stream until either a non-space character is detected, or until atEnd() returns true. This function is useful when reading a stream character by character.

Whitespace characters are all characters for which isSpace() returns true.

See also

operator>>()

status()
Return type:

Status

Returns the status of the text stream.

string()
Return type:

str

Returns the current string assigned to the QTextStream , or None if no string has been assigned.

See also

setString() device()