class QFile¶

The QFile class provides an interface for reading from and writing to files. More…

Inherited by: QTemporaryFile

Synopsis¶

Methods¶

def __init__()
def copy()
def exists()
def link()
def moveToTrash()
def open()
def remove()
def rename()
def setFileName()
def symLinkTarget()

Static functions¶

def copy()
def decodeName()
def encodeName()
def exists()
def link()
def moveToTrash()
def permissions()
def remove()
def rename()
def resize()
def setPermissions()
def symLinkTarget()

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.

QFile is an I/O device for reading and writing text and binary files and resources . A QFile may be used by itself or, more conveniently, with a QTextStream or QDataStream .

The file name is usually passed in the constructor, but it can be set at any time using setFileName() . QFile expects the file separator to be ‘/’ regardless of operating system. The use of other separators (e.g., ‘\’) is not supported.

You can check for a file’s existence using exists() , and remove a file using remove() . (More advanced file system related operations are provided by QFileInfo and QDir .)

The file is opened with open() , closed with close() , and flushed with flush() . Data is usually read and written using QDataStream or QTextStream , but you can also call the QIODevice -inherited functions read() , readLine() , readAll() , write() . QFile also inherits getChar() , putChar() , and ungetChar() , which work one character at a time.

The size of the file is returned by size() . You can get the current file position using pos() , or move to a new file position using seek() . If you’ve reached the end of the file, atEnd() returns true.

Reading Files Directly¶

The following example reads a text file line by line:

file = QFile("in.txt")
if not file.open(QIODevice.ReadOnly | QIODevice.Text):
    return
while not file.atEnd():
    line = file.readLine()
    process_line(line)

The QIODevice::Text flag passed to open() tells Qt to convert Windows-style line terminators (”\r\n”) into C++-style terminators (”\n”). By default, QFile assumes binary, i.e. it doesn’t perform any conversion on the bytes stored in the file.

Using Streams to Read Files¶

The next example uses QTextStream to read a text file line by line:

file = QFile("in.txt")
if not file.open(QIODevice.ReadOnly | QIODevice.Text):
    return
in = QTextStream(file)
while not in.atEnd():
    line = in.readLine()
    process_line(line)

QTextStream takes care of converting the 8-bit data stored on disk into a 16-bit Unicode QString . By default, it assumes that the file is encoded in UTF-8. This can be changed using setEncoding() .

To write text, we can use operator<<(), which is overloaded to take a QTextStream on the left and various data types (including QString ) on the right:

file = QFile("out.txt")
if not file.open(QIODevice.WriteOnly | QIODevice.Text):
    return
out = QTextStream(file)
out << "The magic number is: " << 49 << "\n"

QDataStream is similar, in that you can use operator<<() to write data and operator>>() to read it back. See the class documentation for details.

Signals¶

Unlike other QIODevice implementations, such as QTcpSocket, QFile does not emit the aboutToClose() , bytesWritten() , or readyRead() signals. This implementation detail means that QFile is not suitable for reading and writing certain types of files, such as device files on Unix platforms.

Platform Specific Issues¶

Qt APIs related to I/O use UTF-16 based QStrings to represent file paths. Standard C++ APIs (<cstdio> or <iostream>) or platform-specific APIs however often need a 8-bit encoded path. You can use encodeName() and decodeName() to convert between both representations.

On Unix, there are some special system files (e.g. in /proc) for which size() will always return 0, yet you may still be able to read more data from such a file; the data is generated in direct response to you calling read() . In this case, however, you cannot use atEnd() to determine if there is more data to read (since atEnd() will return true for a file that claims to have size 0). Instead, you should either call readAll() , or call read() or readLine() repeatedly until no more data can be read. The next example uses QTextStream to read /proc/modules line by line:

file = QFile("/proc/modules")
if not file.open(QIODevice.ReadOnly | QIODevice.Text):
    return
in = QTextStream(file)
line = in.readLine()
while not line.isNull():
    process_line(line)
    line = in.readLine()

File permissions are handled differently on Unix-like systems and Windows. In a non writable directory on Unix-like systems, files cannot be created. This is not always the case on Windows, where, for instance, the ‘My Documents’ directory usually is not writable, but it is still possible to create files in it.

Qt’s understanding of file permissions is limited, which affects especially the setPermissions() function. On Windows, Qt will set only the legacy read-only flag, and that only when none of the Write* flags are passed. Qt does not manipulate access control lists (ACLs), which makes this function mostly useless for NTFS volumes. It may still be of use for USB sticks that use VFAT file systems. POSIX ACLs are not manipulated, either.

On Android, some limitations apply when dealing with content URIs :

Access permissions might be needed by prompting the user through the QFileDialog which implements Android’s native file picker .

Aim to follow the Scoped storage guidelines, such as using app specific directories instead of other public external directories. For more information, also see storage best practices .

Due to the design of Qt APIs (e.g. QFile ), it’s not possible to fully integrate the latter APIs with Android’s MediaStore APIs.

See also

QTextStream QDataStream QFileInfo QDir The Qt Resource System

__init__()¶

Constructs a QFile object.

__init__(parent)

Parameters:: parent – QObject

Constructs a new file object with the given parent.

__init__(name)

Parameters:: name – str

Constructs a new file object to represent the file with the given name.

Note

In versions up to and including Qt 6.8, this constructor is implicit, for backward compatibility. Starting from Qt 6.9 this constructor is unconditionally explicit. Users can force this constructor to be explicit even in earlier versions of Qt by defining the QT_EXPLICIT_QFILE_CONSTRUCTION_FROM_PATH macro before including any Qt header.

__init__(name, parent)

Parameters:

name – str
parent – QObject

Constructs a new file object with the given parent to represent the file with the specified name.

copy(newName)¶

Parameters:: newName – str
Return type:: bool

Copies the file named fileName() to newName.

This file is closed before it is copied.

If the copied file is a symbolic link (symlink), the file it refers to is copied, not the link itself. With the exception of permissions, which are copied, no other file metadata is copied.

Returns true if successful; otherwise returns false.

Note that if a file with the name newName already exists, copy() returns false. This means QFile will not overwrite it.

Note

On Android, this operation is not yet supported for content scheme URIs.

See also

setFileName()

static copy(fileName, newName)

Parameters:

fileName – str
newName – str

Return type:

bool

This is an overloaded function.

Copies the file named fileName to newName.

This file is closed before it is copied.

If the copied file is a symbolic link (symlink), the file it refers to is copied, not the link itself. With the exception of permissions, which are copied, no other file metadata is copied.

Returns true if successful; otherwise returns false.

Note that if a file with the name newName already exists, copy() returns false. This means QFile will not overwrite it.

Note

On Android, this operation is not yet supported for content scheme URIs.

See also

rename()

static decodeName(localFileName)¶

Parameters:: localFileName – QByteArray
Return type:: str

This does the reverse of encodeName() using localFileName.

See also

encodeName()

static decodeName(localFileName)

Parameters:: localFileName – str
Return type:: str

This is an overloaded function.

Returns the Unicode version of the given localFileName. See encodeName() for details.

static encodeName(fileName)¶

Parameters:: fileName – str
Return type:: QByteArray

Converts fileName to an 8-bit encoding that you can use in native APIs. On Windows, the encoding is the one from active Windows (ANSI) codepage. On other platforms, this is UTF-8, for macOS in decomposed form (NFD).

See also

decodeName()

exists()¶

Return type:: bool

This is an overloaded function.

Returns true if the file specified by fileName() exists; otherwise returns false.

See also

fileName() setFileName()

static exists(fileName)

Parameters:: fileName – str
Return type:: bool

Returns true if the file specified by fileName exists; otherwise returns false.

Note

If fileName is a symlink that points to a non-existing file, false is returned.

link(newName)¶

Parameters:: newName – str
Return type:: bool

Creates a link named linkName that points to the file currently specified by fileName() . What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true if successful; otherwise returns false.

This function will not overwrite an already existing entity in the file system; in this case, link() will return false and set error() to return RenameError .

Note

To create a valid link on Windows, linkName must have a .lnk file extension.

See also

setFileName()

static link(fileName, newName)

Parameters:

fileName – str
newName – str

Return type:

bool

This is an overloaded function.

Creates a link named linkName that points to the file fileName. What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true if successful; otherwise returns false.

See also

link()

moveToTrash()¶

Return type:: bool

Moves the file specified by fileName() to the trash. Returns true if successful, and sets the fileName() to the path at which the file can be found within the trash; otherwise returns false.

The time for this function to run is independent of the size of the file being trashed. If this function is called on a directory, it may be proportional to the number of files being trashed. If the current fileName() points to a symbolic link, this function will move the link to the trash, possibly breaking it, not the target of the link.

This function uses the Windows and macOS APIs to perform the trashing on those two operating systems. Elsewhere (Unix systems), this function implements the FreeDesktop.org Trash specification version 1.0.

Note

When using the FreeDesktop.org Trash implementation, this function will fail if it is unable to move the files to the trash location by way of file renames and hardlinks. This condition arises if the file being trashed resides on a volume (mount point) on which the current user does not have permission to create the .Trash directory, or with some unusual filesystem types or configurations (such as sub-volumes that aren’t themselves mount points).

Note

On systems where the system API doesn’t report the location of the file in the trash, fileName() will be set to the null string once the file has been moved. On systems that don’t have a trash can, this function always returns false.

static moveToTrash(fileName[, pathInTrash=None])

Parameters:

fileName – str
pathInTrash – str

Return type:

bool

This is an overloaded function.

Moves the file specified by fileName to the trash. Returns true if successful, and sets pathInTrash (if provided) to the path at which the file can be found within the trash; otherwise returns false.

Note

On systems where the system API doesn’t report the path of the file in the trash, pathInTrash will be set to the null string once the file has been moved. On systems that don’t have a trash can, this function always returns false.

open(flags, permissions)¶

Parameters:

flags – Combination of OpenModeFlag
permissions – Combination of Permission

Return type:

bool

This is an overloaded function.

If the file does not exist and mode implies creating it, it is created with the specified permissions.

On POSIX systems the actual permissions are influenced by the value of umask.

On Windows the permissions are emulated using ACLs. These ACLs may be in non-canonical order when the group is granted less permissions than others. Files and directories with such permissions will generate warnings when the Security tab of the Properties dialog is opened. Granting the group all permissions granted to others avoids such warnings.

See also

OpenMode setFileName() QT_USE_NODISCARD_FILE_OPEN

open(fd, ioFlags[, handleFlags=QFileDevice.FileHandleFlag.DontCloseHandle])

Parameters:

fd – int
ioFlags – Combination of OpenModeFlag
handleFlags – Combination of FileHandleFlag

Return type:

bool

This is an overloaded function.

Opens the existing file descriptor fd in the given mode. handleFlags may be used to specify additional options. Returns true if successful; otherwise returns false.

When a QFile is opened using this function, behaviour of close() is controlled by the AutoCloseHandle flag. If AutoCloseHandle is specified, and this function succeeds, then calling close() closes the adopted handle. Otherwise, close() does not actually close the file, but only flushes it.

Warning

If fd is not a regular file, e.g, it is 0 (stdin), 1 (stdout), or 2 (stderr), you may not be able to seek() . In those cases, size() returns 0. See isSequential() for more information.

Warning

Since this function opens the file without specifying the file name, you cannot use this QFile with a QFileInfo .

See also

close() QT_USE_NODISCARD_FILE_OPEN

static permissions(filename)¶

Parameters:: filename – str
Return type:: Combination of Permission

This is an overloaded function.

Returns the complete OR-ed together combination of QFile::Permission for fileName.

remove()¶

Return type:: bool

Removes the file specified by fileName() . Returns true if successful; otherwise returns false.

The file is closed before it is removed.

See also

setFileName()

static remove(fileName)

Parameters:: fileName – str
Return type:: bool

This is an overloaded function.

Removes the file specified by the fileName given.

Returns true if successful; otherwise returns false.

See also

remove()

rename(newName)¶

Parameters:: newName – str
Return type:: bool

Renames the file currently specified by fileName() to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, rename() returns false (i.e., QFile will not overwrite it).

The file is closed before it is renamed.

If the rename operation fails, Qt will attempt to copy this file’s contents to newName, and then remove this file, keeping only newName. If that copy operation fails or this file can’t be removed, the destination file newName is removed to restore the old state.

See also

setFileName()

static rename(oldName, newName)

Parameters:

oldName – str
newName – str

Return type:

bool

This is an overloaded function.

Renames the file oldName to newName. Returns true if successful; otherwise returns false.

If a file with the name newName already exists, rename() returns false (i.e., QFile will not overwrite it).

See also

rename()

static resize(filename, sz)¶

Parameters:

filename – str
sz – int

Return type:

bool

This is an overloaded function.

Sets fileName to size (in bytes) sz. Returns true if the resize succeeds; false otherwise. If sz is larger than fileName currently is the new bytes will be set to 0, if sz is smaller the file is simply truncated.

Warning

This function can fail if the file doesn’t exist.

See also

resize()

setFileName(name)¶

Parameters:: name – str

Warning

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

Sets the name of the file. The name can have no path, a relative path, or an absolute path.

Do not call this function if the file has already been opened.

If the file name has no path or a relative path, the path used will be the application’s current directory path at the time of the open() ** call.

Example:

file = QFile()
QDir.setCurrent("/tmp")
file.setFileName("readme.txt")
QDir.setCurrent("/home")
file.open(QIODevice.ReadOnly) # opens "/home/readme.txt" under Unix

Note that the directory separator “/” works for all operating systems supported by Qt.

See also

fileName() QFileInfo QDir

static setPermissions(filename, permissionSpec)¶

Parameters:

filename – str
permissionSpec – Combination of Permission

Return type:

bool

This is an overloaded function.

Sets the permissions for fileName file to permissions.

symLinkTarget()¶

Return type:: str

This is an overloaded function.

Returns the absolute path of the file or directory a symlink (or shortcut on Windows) points to, or a an empty string if the object isn’t a symbolic link.

This name may not represent an existing file; it is only a string. exists() returns true if the symlink points to an existing file.

See also

fileName() setFileName()

static symLinkTarget(fileName)

Parameters:: fileName – str
Return type:: str

Returns the absolute path of the file or directory referred to by the symlink (or shortcut on Windows) specified by fileName, or returns an empty string if the fileName does not correspond to a symbolic link.

This name may not represent an existing file; it is only a string. exists() returns true if the symlink points to an existing file.