QCanDbcFileParse load error

[dhagrow]

I'm trying to use QCanDbcFileParser from PySide6, but I can't seem to load anything. Below is some sample code which loads the DBC with QFile first with no problem.

import argparse
import sys

from PySide6.QtCore import QFile
from PySide6.QtSerialBus import QCanDbcFileParser


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("dbc_file")

    args = parser.parse_args()

    parse(args.dbc_file)


def parse(dbc_file):
    f = QFile(dbc_file)
    if not f.open(QFile.OpenModeFlag.ReadOnly):
        sys.exit(f"QFile.open: {f.errorString()}")

    print("DBC File:")
    print(bytes(f.readAll()).decode())

    parser = QCanDbcFileParser()
    if not parser.parse(dbc_file):
        sys.exit(f"QCanDbcFileParser.parse: {parser.errorString()}")


if __name__ == "__main__":
    main()

And here is the output:

DBC File:
BO_ 399 STEER_STATUS: 7 EPS
 SG_ STEER_TORQUE_SENSOR : 7|16@0- (-1,0) [-31000|31000] "tbd" EON
 SG_ STEER_ANGLE_RATE : 23|16@0- (-0.1,0) [-31000|31000] "deg/s" EON
 SG_ STEER_STATUS : 39|4@0+ (1,0) [0|15] "" EON
 SG_ STEER_CONTROL_ACTIVE : 35|1@0+ (1,0) [0|1] "" EON
 SG_ STEER_CONFIG_INDEX : 43|4@0+ (1,0) [0|15] "" EON
 SG_ COUNTER : 53|2@0+ (1,0) [0|3] "" EON
 SG_ CHECKSUM : 51|4@0+ (1,0) [0|15] "" EON

BO_ 420 VSA_STATUS: 8 VSA
 SG_ ESP_DISABLED : 28|1@0+ (1,0) [0|1] "" EON
 SG_ USER_BRAKE : 7|16@0+ (0.015625,-1.609375) [0|1000] "" EON
 SG_ BRAKE_HOLD_ACTIVE : 46|1@0+ (1,0) [0|1] "" EON
 SG_ BRAKE_HOLD_ENABLED : 45|1@0+ (1,0) [0|1] "" EON
 SG_ COUNTER : 61|2@0+ (1,0) [0|3] "" EON
 SG_ CHECKSUM : 59|4@0+ (1,0) [0|15] "" EON

BO_ 464 WHEEL_SPEEDS: 8 VSA
 SG_ WHEEL_SPEED_FL : 7|15@0+ (0.01,0) [0|250] "kph" EON
 SG_ WHEEL_SPEED_FR : 8|15@0+ (0.01,0) [0|250] "kph" EON
 SG_ WHEEL_SPEED_RL : 25|15@0+ (0.01,0) [0|250] "kph" EON
 SG_ WHEEL_SPEED_RR : 42|15@0+ (0.01,0) [0|250] "kph" EON
 SG_ CHECKSUM : 59|4@0+ (1,0) [0|3] "" EON

QCanDbcFileParser.parse: No such file or directory

The error doesn't help much to determine the problem. Posting here first in case this is an issue with the PySide6 bindings.

[SGaist]

Hi and welcome to devnet,

You're using it wrong. That method expects a file path. Maybe you meant to use parseData ?

[jsulm]

@SGaist As far as I can see OP is passing a path to the file

[jsulm]

@dhagrow Why don't you do what the documentation suggests?
https://doc.qt.io/qt-6/qcandbcfileparser.html#parse
"If the parsing failed, call the error() and errorString() methods to get the information about the error."

[JonB]

@jsulm said in QCanDbcFileParse load error:

"If the parsing failed, call the error() and errorString() methods to get the information about the error."

OP already does!

if not parser.parse(dbc_file):
    sys.exit(f"QCanDbcFileParser.parse: {parser.errorString()}")
// Output:
QCanDbcFileParser.parse: No such file or directory

I think OP is asking: He shows QFile::open()ing the file correctly and shows its contents, so why does he get a "no such file or directory" from parser.parse(dbc_file) on same file path? I don't know.

@dhagrow
FWIW, bool QCanDbcFileParser::parse(const QString &fileName)

Note: This method expects the file contents to be encoded in UTF-8. If the file has a different encoding, decode it first, and use parseData() to extract the DBC information.

You might try passing your f.readAll()).decode() to bool QCanDbcFileParser::parseData(QStringView data) to see whether that succeeds? I do not know how that relates to a "no such file" failure from QCanDbcFileParser.parse().

[jsulm]

@JonB said in QCanDbcFileParse load error:

OP already does!

You're right, did not see that in the string formatting :-)

[SGaist]

@jsulm said in QCanDbcFileParse load error:

@SGaist As far as I can see OP is passing a path to the file

Indeed, I misread the reading/printing and parse call !

@dhagrow, @JonB has a point with regard to UTF-8.

Also, on which OS are you seeing this issue ?

[JonB]

@SGaist said in QCanDbcFileParse load error:

@dhagrow, @JonB has a point with regard to UTF-8.

Except that error "no such file or directory" does not sound like that, does sound like it's not finding the file. Or a strange message.

[SGaist]

@JonB said in QCanDbcFileParse load error:

@SGaist said in QCanDbcFileParse load error:

@dhagrow, @JonB has a point with regard to UTF-8.

Except that error "no such file or directory" does not sound like that, does sound like it's not finding the file. Or a strange message.

Indeed, I was just adding more weight with regard to using parseData which was related to my original question about it although it was mainly because I misread the code sample.

[dhagrow]

QCanDbcFileParser.parseData() does indeed work! Thanks for pointing that out, I hadn't noticed that method. I'm not sure why the encoding would matter. The contents are ASCII, which should be decoded by UTF-8 with no problem.

Nothing obvious strikes me from the source here, but I guess QString is not included in PySide, so I can't easily check.

It does seem like there should be a better error there, but this solves my immediate problem, and hopefully helps anyone else that runs into it. For the record, I'm on Linux. Thanks again!

[JonB]

@dhagrow
Yes, parseData() will work, the question is why parser.parse(dbc_file) does not seem to open the file from its name. Just try making dbc_file be the correct full path to the file (not just plain "dbc_file") and check whether that makes a difference?

[dhagrow]

I get this error instead when I pass in a full path, or even when I use any slash, e.g. ./test.dbc.

QCanDbcFileParser.parse: file to open is a directory

[JonB]

@dhagrow
Well that's very odd if it's a file and is reported as an open directory failure.
And also odd but maybe significant if the path alters message from "No such file or directory" to "file to open is a directory".

[dhagrow]

I think I found the problem. I noticed that there's an overload for QCanDbcFileParser.parse that takes a QStringList. It turns out that it works if I pass in ['test.dbc']! I then tried ['t'] and ['.'] and get the same errors I was getting above. It seems PySide is wrapping the overloaded method.

[JonB]

@dhagrow
But I thought you started from passing a sting, like "dbc_file". That should match parse(fileName) where fileName – str. I don't know exactly what you tried? Where did you get dbc_file varibale value from? Be careful of you prompted the user for it with QFileDialog.getOpenFileName(), that returns a list, not just the filename.

I don't know whether you are now saying you are sorted or not.

[dhagrow]

Yes, I am sorted. The QCanDbcFileParser.parseData option was all I needed, but I see that I can also use QCanDbcFileParser.parse if I pass in the file name in a list.

"dbc_file" came from a command-line argument, so effectively I was making the call like: parser.parse("test.dbc"). That appears to treat the string like a list, so with test.dbc it would try to open t, and with ./test.dbc it would try ., both of which align with the errors I was seeing. I now see that I can make the call like: parser.parse(["test.dbc"]), which works.

Basically, what I am saying is that PySide is not calling QCanDbcFileParser::parse(QString). It is actually calling QCanDbcFileParser::parse(QStringList).

[JonB]

@dhagrow Fine for a workaround, but if what you say is true that would apparently be a bug in PySide.

[SGaist]

I agree with @JonB. A Python string shares some interfaces with the list class however it should not trigger that issue. Something is wrong with the binding. You should open a ticket on the bug report system.

[dhagrow]

Issue created: https://bugreports.qt.io/browse/PYSIDE-3017