QCommandLineParser

The QCommandLineParser class provides a means for handling the command line options. More

Inheritance diagram of PySide2.QtCore.QCommandLineParser

New in version 5.2.

Synopsis

Functions

Detailed Description

QCoreApplication provides the command-line arguments as a simple list of strings. QCommandLineParser provides the ability to define a set of options, parse the command-line arguments, and store which options have actually been used, as well as option values.

Any argument that isn’t an option (i.e. doesn’t start with a - ) is stored as a “positional argument”.

The parser handles short names, long names, more than one name for the same option, and option values.

Options on the command line are recognized as starting with a single or double - character(s). The option - (single dash alone) is a special case, often meaning standard input, and not treated as an option. The parser will treat everything after the option -- (double dash) as positional arguments.

Short options are single letters. The option v would be specified by passing -v on the command line. In the default parsing mode, short options can be written in a compact form, for instance -abc is equivalent to -a -b -c . The parsing mode for can be set to ParseAsLongOptions , in which case -abc will be parsed as the long option abc .

Long options are more than one letter long and cannot be compacted together. The long option verbose would be passed as --verbose or -verbose .

Passing values to options can be done using the assignment operator: -v=value --verbose=value , or a space: -v value --verbose value , i.e. the next argument is used as value (even if it starts with a - ).

The parser does not support optional values - if an option is set to require a value, one must be present. If such an option is placed last and has no value, the option will be treated as if it had not been specified.

The parser does not automatically support negating or disabling long options by using the format --disable-option or --no-option . However, it is possible to handle this case explicitly by making an option with no-option as one of its names, and handling the option explicitly.

Example:

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    QCoreApplication::setApplicationName("my-copy-program");
    QCoreApplication::setApplicationVersion("1.0");

    QCommandLineParser parser;
    parser.setApplicationDescription("Test helper");
    parser.addHelpOption();
    parser.addVersionOption();
    parser.addPositionalArgument("source", QCoreApplication::translate("main", "Source file to copy."));
    parser.addPositionalArgument("destination", QCoreApplication::translate("main", "Destination directory."));

    // A boolean option with a single name (-p)
    QCommandLineOption showProgressOption("p", QCoreApplication::translate("main", "Show progress during copy"));
    parser.addOption(showProgressOption);

    // A boolean option with multiple names (-f, --force)
    QCommandLineOption forceOption(QStringList() << "f" << "force",
            QCoreApplication::translate("main", "Overwrite existing files."));
    parser.addOption(forceOption);

    // An option with a value
    QCommandLineOption targetDirectoryOption(QStringList() << "t" << "target-directory",
            QCoreApplication::translate("main", "Copy all source files into <directory>."),
            QCoreApplication::translate("main", "directory"));
    parser.addOption(targetDirectoryOption);

    // Process the actual command line arguments given by the user
    parser.process(app);

    const QStringList args = parser.positionalArguments();
    // source is args.at(0), destination is args.at(1)

    bool showProgress = parser.isSet(showProgressOption);
    bool force = parser.isSet(forceOption);
    QString targetDir = parser.value(targetDirectoryOption);
    // ...
}

If your compiler supports the C++11 standard, the three addOption() calls in the above example can be simplified:

parser.addOptions({
    // A boolean option with a single name (-p)
    {"p",
        QCoreApplication::translate("main", "Show progress during copy")},
    // A boolean option with multiple names (-f, --force)
    {{"f", "force"},
        QCoreApplication::translate("main", "Overwrite existing files.")},
    // An option with a value
    {{"t", "target-directory"},
        QCoreApplication::translate("main", "Copy all source files into <directory>."),
        QCoreApplication::translate("main", "directory")},
});

Known limitation: the parsing of Qt options inside QCoreApplication and subclasses happens before QCommandLineParser exists, so it can’t take it into account. This means any option value that looks like a builtin Qt option, will be treated by QCoreApplication as a builtin Qt option. Example: --profile -reverse will lead to QGuiApplication seeing the -reverse option set, and removing it from arguments() before QCommandLineParser defines the profile option and parses the command line.

How to Use QCommandLineParser in Complex Applications

In practice, additional error checking needs to be performed on the positional arguments and option values. For example, ranges of numbers should be checked.

It is then advisable to introduce a function to do the command line parsing which takes a struct or class receiving the option values returning an enumeration representing the result. The dnslookup example of the QtNetwork module illustrates this:

struct DnsQuery
{
    DnsQuery() : type(QDnsLookup::A) {}

    QDnsLookup::Type type;
    QHostAddress nameServer;
    QString name;
};


enum CommandLineParseResult
{
    CommandLineOk,
    CommandLineError,
    CommandLineVersionRequested,
    CommandLineHelpRequested
};

CommandLineParseResult parseCommandLine(QCommandLineParser &parser, DnsQuery *query, QString *errorMessage)
{
    parser.setSingleDashWordOptionMode(QCommandLineParser::ParseAsLongOptions);
    const QCommandLineOption nameServerOption("n", "The name server to use.", "nameserver");
    parser.addOption(nameServerOption);
    const QCommandLineOption typeOption("t", "The lookup type.", "type");
    parser.addOption(typeOption);
    parser.addPositionalArgument("name", "The name to look up.");
    const QCommandLineOption helpOption = parser.addHelpOption();
    const QCommandLineOption versionOption = parser.addVersionOption();

    if (!parser.parse(QCoreApplication::arguments())) {
        *errorMessage = parser.errorText();
        return CommandLineError;
    }

    if (parser.isSet(versionOption))
        return CommandLineVersionRequested;

    if (parser.isSet(helpOption))
        return CommandLineHelpRequested;

    if (parser.isSet(nameServerOption)) {
        const QString nameserver = parser.value(nameServerOption);
        query->nameServer = QHostAddress(nameserver);
        if (query->nameServer.isNull() || query->nameServer.protocol() == QAbstractSocket::UnknownNetworkLayerProtocol) {
            *errorMessage = "Bad nameserver address: " + nameserver;
            return CommandLineError;
        }
    }

    if (parser.isSet(typeOption)) {
        const QString typeParameter = parser.value(typeOption);
        const int type = typeFromParameter(typeParameter.toLower());
        if (type < 0) {
            *errorMessage = "Bad record type: " + typeParameter;
            return CommandLineError;
        }
        query->type = static_cast<QDnsLookup::Type>(type);
    }

    const QStringList positionalArguments = parser.positionalArguments();
    if (positionalArguments.isEmpty()) {
        *errorMessage = "Argument 'name' missing.";
        return CommandLineError;
    }
    if (positionalArguments.size() > 1) {
        *errorMessage = "Several 'name' arguments specified.";
        return CommandLineError;
    }
    query->name = positionalArguments.first();

    return CommandLineOk;
}

In the main function, help should be printed to the standard output if the help option was passed and the application should return the exit code 0.

If an error was detected, the error message should be printed to the standard error output and the application should return an exit code other than 0.

QCoreApplication::setApplicationVersion(QT_VERSION_STR);
QCoreApplication::setApplicationName(QCoreApplication::translate("QDnsLookupExample", "DNS Lookup Example"));
QCommandLineParser parser;
parser.setApplicationDescription(QCoreApplication::translate("QDnsLookupExample", "An example demonstrating the class QDnsLookup."));
DnsQuery query;
QString errorMessage;
switch (parseCommandLine(parser, &query, &errorMessage)) {
case CommandLineOk:
    break;
case CommandLineError:
    fputs(qPrintable(errorMessage), stderr);
    fputs("\n\n", stderr);
    fputs(qPrintable(parser.helpText()), stderr);
    return 1;
case CommandLineVersionRequested:
    printf("%s %s\n", qPrintable(QCoreApplication::applicationName()),
           qPrintable(QCoreApplication::applicationVersion()));
    return 0;
case CommandLineHelpRequested:
    parser.showHelp();
    Q_UNREACHABLE();
}

A special case to consider here are GUI applications on Windows and mobile platforms. These applications may not use the standard output or error channels since the output is either discarded or not accessible.

On Windows, QCommandLineParser uses message boxes to display usage information and errors if no console window can be obtained.

For other platforms, it is recommended to display help texts and error messages using a QMessageBox . To preserve the formatting of the help text, rich text with <pre> elements should be used:

switch (parseCommandLine(parser, &query, &errorMessage)) {
case CommandLineOk:
    break;
case CommandLineError:
    QMessageBox::warning(0, QGuiApplication::applicationDisplayName(),
                         "<html><head/><body><h2>" + errorMessage + "</h2><pre>"
                         + parser.helpText() + "</pre></body></html>");
    return 1;
case CommandLineVersionRequested:
    QMessageBox::information(0, QGuiApplication::applicationDisplayName(),
                             QGuiApplication::applicationDisplayName() + ' '
                             + QCoreApplication::applicationVersion());
    return 0;
case CommandLineHelpRequested:
    QMessageBox::warning(0, QGuiApplication::applicationDisplayName(),
                         "<html><head/><body><pre>"
                         + parser.helpText() + "</pre></body></html>");
    return 0;
}

However, this does not apply to the dnslookup example, because it is a console application.

class QCommandLineParser

Constructs a command line parser object.

PySide2.QtCore.QCommandLineParser.SingleDashWordOptionMode

This enum describes the way the parser interprets command-line options that use a single dash followed by multiple letters, as as -abc .

Constant

Description

QCommandLineParser.ParseAsCompactedShortOptions

-abc is interpreted as -a -b -c, i.e. as three short options that have been compacted on the command-line, if none of the options take a value. If a takes a value, then it is interpreted as -a bc, i.e. the short option a followed by the value bc. This is typically used in tools that behave like compilers, in order to handle options such as -DDEFINE=VALUE or -I/include/path. This is the default parsing mode. New applications are recommended to use this mode.

QCommandLineParser.ParseAsLongOptions

-abc is interpreted as --abc, i.e. as the long option named abc. This is how Qt’s own tools (uic, rcc…) have always been parsing arguments. This mode should be used for preserving compatibility in applications that were parsing arguments in such a way. There is an exception if the a option has the ShortOptionStyle flag set, in which case it is still interpreted as -a bc.

PySide2.QtCore.QCommandLineParser.OptionsAfterPositionalArgumentsMode

This enum describes the way the parser interprets options that occur after positional arguments.

Constant

Description

QCommandLineParser.ParseAsOptions

application argument --opt -t is interpreted as setting the options opt and t, just like application --opt -t argument would do. This is the default parsing mode. In order to specify that --opt and -t are positional arguments instead, the user can use --, as in application argument -- --opt -t.

QCommandLineParser.ParseAsPositionalArguments

application argument --opt is interpreted as having two positional arguments, argument and --opt. This mode is useful for executables that aim to launch other executables (e.g. wrappers, debugging tools, etc.) or that support internal commands followed by options for the command. argument is the name of the command, and all options occurring after it can be collected and parsed by another command line parser, possibly in another executable.

New in version 5.6.

PySide2.QtCore.QCommandLineParser.addHelpOption()
Return type

QCommandLineOption

Adds the help option (-h , --help and -? on Windows) as well as an option --help-all to include Qt-specific options in the output.

These options are handled automatically by QCommandLineParser .

Remember to use setApplicationDescription to set the application description, which will be displayed when this option is used.

Example:

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    QCoreApplication::setApplicationName("my-copy-program");
    QCoreApplication::setApplicationVersion("1.0");

    QCommandLineParser parser;
    parser.setApplicationDescription("Test helper");
    parser.addHelpOption();
    parser.addVersionOption();
    parser.addPositionalArgument("source", QCoreApplication::translate("main", "Source file to copy."));
    parser.addPositionalArgument("destination", QCoreApplication::translate("main", "Destination directory."));

    // A boolean option with a single name (-p)
    QCommandLineOption showProgressOption("p", QCoreApplication::translate("main", "Show progress during copy"));
    parser.addOption(showProgressOption);

    // A boolean option with multiple names (-f, --force)
    QCommandLineOption forceOption(QStringList() << "f" << "force",
            QCoreApplication::translate("main", "Overwrite existing files."));
    parser.addOption(forceOption);

    // An option with a value
    QCommandLineOption targetDirectoryOption(QStringList() << "t" << "target-directory",
            QCoreApplication::translate("main", "Copy all source files into <directory>."),
            QCoreApplication::translate("main", "directory"));
    parser.addOption(targetDirectoryOption);

    // Process the actual command line arguments given by the user
    parser.process(app);

    const QStringList args = parser.positionalArguments();
    // source is args.at(0), destination is args.at(1)

    bool showProgress = parser.isSet(showProgressOption);
    bool force = parser.isSet(forceOption);
    QString targetDir = parser.value(targetDirectoryOption);
    // ...
}

Returns the option instance, which can be used to call isSet() .

PySide2.QtCore.QCommandLineParser.addOption(commandLineOption)
Parameters

commandLineOptionQCommandLineOption

Return type

bool

Adds the option option to look for while parsing.

Returns true if adding the option was successful; otherwise returns false .

Adding the option fails if there is no name attached to the option, or the option has a name that clashes with an option name added before.

PySide2.QtCore.QCommandLineParser.addOptions(options)
Parameters

options

Return type

bool

Adds the options to look for while parsing. The options are specified by the parameter options .

Returns true if adding all of the options was successful; otherwise returns false .

See the documentation for addOption() for when this function may fail.

PySide2.QtCore.QCommandLineParser.addPositionalArgument(name, description[, syntax=""])
Parameters
  • name – unicode

  • description – unicode

  • syntax – unicode

Defines an additional argument to the application, for the benefit of the help text.

The argument name and description will appear under the Arguments: section of the help. If syntax is specified, it will be appended to the Usage line, otherwise the name will be appended.

Example:

// Usage: image-editor file
//
// Arguments:
//   file                  The file to open.
parser.addPositionalArgument("file", QCoreApplication::translate("main", "The file to open."));

// Usage: web-browser [urls...]
//
// Arguments:
//   urls                URLs to open, optionally.
parser.addPositionalArgument("urls", QCoreApplication::translate("main", "URLs to open, optionally."), "[urls...]");

// Usage: cp source destination
//
// Arguments:
//   source                Source file to copy.
//   destination           Destination directory.
parser.addPositionalArgument("source", QCoreApplication::translate("main", "Source file to copy."));
parser.addPositionalArgument("destination", QCoreApplication::translate("main", "Destination directory."));
PySide2.QtCore.QCommandLineParser.addVersionOption()
Return type

QCommandLineOption

Adds the -v / --version option, which displays the version string of the application.

This option is handled automatically by QCommandLineParser .

You can set the actual version string by using setApplicationVersion() .

Returns the option instance, which can be used to call isSet() .

PySide2.QtCore.QCommandLineParser.applicationDescription()
Return type

unicode

Returns the application description set in setApplicationDescription() .

PySide2.QtCore.QCommandLineParser.clearPositionalArguments()

Clears the definitions of additional arguments from the help text.

This is only needed for the special case of tools which support multiple commands with different options. Once the actual command has been identified, the options for this command can be defined, and the help text for the command can be adjusted accordingly.

Example:

QCoreApplication app(argc, argv);
QCommandLineParser parser;

parser.addPositionalArgument("command", "The command to execute.");

// Call parse() to find out the positional arguments.
parser.parse(QCoreApplication::arguments());

const QStringList args = parser.positionalArguments();
const QString command = args.isEmpty() ? QString() : args.first();
if (command == "resize") {
    parser.clearPositionalArguments();
    parser.addPositionalArgument("resize", "Resize the object to a new size.", "resize [resize_options]");
    parser.addOption(QCommandLineOption("size", "New size.", "new_size"));
    parser.process(app);
    // ...
}

/*
This code results in context-dependent help:

$ tool --help
Usage: tool command

Arguments:
  command  The command to execute.

$ tool resize --help
Usage: tool resize [resize_options]

Options:
  --size <size>  New size.

Arguments:
  resize         Resize the object to a new size.
*/
PySide2.QtCore.QCommandLineParser.errorText()
Return type

unicode

Returns a translated error text for the user. This should only be called when parse() returns false .

PySide2.QtCore.QCommandLineParser.helpText()
Return type

unicode

Returns a string containing the complete help information.

See also

showHelp()

PySide2.QtCore.QCommandLineParser.isSet(option)
Parameters

optionQCommandLineOption

Return type

bool

PySide2.QtCore.QCommandLineParser.isSet(name)
Parameters

name – unicode

Return type

bool

PySide2.QtCore.QCommandLineParser.optionNames()
Return type

list of strings

Returns a list of option names that were found.

This returns a list of all the recognized option names found by the parser, in the order in which they were found. For any long options that were in the form {–option=value}, the value part will have been dropped.

The names in this list do not include the preceding dash characters. Names may appear more than once in this list if they were encountered more than once by the parser.

Any entry in the list can be used with value() or with values() to get any relevant option values.

PySide2.QtCore.QCommandLineParser.parse(arguments)
Parameters

arguments – list of strings

Return type

bool

Parses the command line arguments .

Most programs don’t need to call this, a simple call to process() is enough.

is more low-level, and only does the parsing. The application will have to take care of the error handling, using errorText() if returns false . This can be useful for instance to show a graphical error message in graphical programs.

Calling instead of process() can also be useful in order to ignore unknown options temporarily, because more option definitions will be provided later on (depending on one of the arguments), before calling process() .

Don’t forget that arguments must start with the name of the executable (ignored, though).

Returns false in case of a parse error (unknown option or missing value); returns true otherwise.

See also

process()

PySide2.QtCore.QCommandLineParser.positionalArguments()
Return type

list of strings

Returns a list of positional arguments.

These are all of the arguments that were not recognized as part of an option.

PySide2.QtCore.QCommandLineParser.process(app)
Parameters

appQCoreApplication

PySide2.QtCore.QCommandLineParser.process(arguments)
Parameters

arguments – list of strings

PySide2.QtCore.QCommandLineParser.setApplicationDescription(description)
Parameters

description – unicode

Sets the application description shown by helpText() .

PySide2.QtCore.QCommandLineParser.setOptionsAfterPositionalArgumentsMode(mode)
Parameters

modeOptionsAfterPositionalArgumentsMode

Sets the parsing mode to parsingMode . This must be called before process() or parse() .

PySide2.QtCore.QCommandLineParser.setSingleDashWordOptionMode(parsingMode)
Parameters

parsingModeSingleDashWordOptionMode

Sets the parsing mode to singleDashWordOptionMode . This must be called before process() or parse() .

PySide2.QtCore.QCommandLineParser.showHelp([exitCode=0])
Parameters

exitCodeint

Displays the help information, and exits the application. This is automatically triggered by the –help option, but can also be used to display the help when the user is not invoking the application correctly. The exit code is set to exitCode . It should be set to 0 if the user requested to see the help, and to any other value in case of an error.

See also

helpText()

PySide2.QtCore.QCommandLineParser.showVersion()

Displays the version information from applicationVersion() , and exits the application. This is automatically triggered by the –version option, but can also be used to display the version when not using process() . The exit code is set to EXIT_SUCCESS (0).

PySide2.QtCore.QCommandLineParser.unknownOptionNames()
Return type

list of strings

Returns a list of unknown option names.

This list will include both long an short name options that were not recognized. For any long options that were in the form {–option=value}, the value part will have been dropped and only the long name is added.

The names in this list do not include the preceding dash characters. Names may appear more than once in this list if they were encountered more than once by the parser.

See also

optionNames()

PySide2.QtCore.QCommandLineParser.value(option)
Parameters

optionQCommandLineOption

Return type

unicode

PySide2.QtCore.QCommandLineParser.value(name)
Parameters

name – unicode

Return type

unicode

PySide2.QtCore.QCommandLineParser.values(option)
Parameters

optionQCommandLineOption

Return type

list of strings

PySide2.QtCore.QCommandLineParser.values(name)
Parameters

name – unicode

Return type

list of strings