🔒 Variable magically becomes None when trying to assign it

[analog aurora]

Hi, I never encountered something like this, any ideas?

print(self.global_target_image != None) # is not None
print(dir(self.global_target_image)) # calibration_data in dir
print(self.global_target_image.calibration_data) # yup, it exists
data = self.global_target_image.calibration_data # global_target_image is now None?

Log:

True
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__firstlineno__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__static_attributes__', '__str__', '__subclasshook__', 'asset_folder', 'blockSignals', 'calibration_data', 'camera_number', 'childEvent', 'children', 'connect', 'connectNotify', 'crop', 'customEvent', 'deleteLater', 'destroyed', 'disconnect', 'disconnectNotify', 'dumpObjectInfo', 'dumpObjectTree', 'dynamicPropertyNames', 'emit', 'event', 'eventFilter', 'export', 'export_path', 'findChild', 'findChildren', 'format', 'generate_preview', 'get_export_path', 'get_target_calibration_data', 'global_target_image', 'image_type', 'inherits', 'installEventFilter', 'isQuickItemType', 'isSignalConnected', 'isWidgetType', 'isWindowType', 'iteration', 'killTimer', 'mark', 'metaObject', 'moveToThread', 'name', 'objectName', 'objectNameChanged', 'original_path', 'parent', 'property', 'raw_path', 'receivers', 'removeEventFilter', 'scale_factor', 'scan', 'scan_finished', 'sender', 'senderSignalIndex', 'sequence', 'setObjectName', 'setParent', 'setProperty', 'set_mark', 'set_status', 'signalsBlocked', 'src_grey', 'startTimer', 'staticMetaObject', 'status', 'target_image', 'thread', 'timerEvent', 'tr', 'tree_item']
<api.calibration_data.CalibrationData object at 0x00000201F6F71FD0>
ERROR:root:'NoneType' object has no attribute 'calibration_data'

[rose reef]

@analog aurora

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[ripe crane]

Is this from a public library? that way i could take a looko at it

[analog aurora]

Nope, this is my own code, I'm assigning global_target_image once at the start, from another Class.

def assign_calibration_targets(self):
        targets = self.calibration_folder.targets

        for img in self.calibration_folder.image_list:
            img.global_target_image = self.calibration_folder.image_list[0]
        ...
        for non_target in non_targets:
            non_target.target_image = get_first_by(
                targets, lambda x: x.camera_number == non_target.camera_number and x.iteration == 1
            )

It never gets re-assigned or touched again

[jaunty crow]

and what does the implementation and assignment to self.global_target_image look like in the class?

[jaunty crow]

what happens if you change your code to

print(self.global_target_image != None) # is not None
print(dir(self.global_target_image)) # calibration_data in dir
data = self.global_target_image.calibration_data
print(data)
```?

also, is .calibration_data an attribute or a property of the api.calibration_data.CalibrationData class?

[analog aurora]

class Image(QObject):
    scan_finished = Signal(ImageStatus)

    def __init__(self, raw_path: Path):
        super().__init__()
        ...

        self.target_image: Image = None
        self.global_target_image: Image = None
        self.calibration_data: CalibrationData = None

Here's target_image and global_target_image

For some reason, when I also assign target_image, global_target_image, no longer throws the error, which confuses me more

def assign_calibration_targets(self):
    targets = self.calibration_folder.targets

    for img in self.calibration_folder.image_list:
        img.global_target_image = self.calibration_folder.image_list[0]
        img.target_image = self.calibration_folder.image_list[0]

[analog aurora]

I get the same issue

[jaunty crow]

i was thinking if it was something that could only be read once and that it would then be consumed or something along those lines

[analog aurora]

yeah I have no idea
both target_image and global_target_image are pretty much the same thing, I don't see why one causes issues and not the other 🙁

[jaunty crow]

it's very hard for us to troubleshoot the issue when only getting bits and pieces of the code without much context, if you are prepared to share much more of your code it would be a lot easier to be able to spot any potential issues

[rose reef]

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[analog aurora]

These should be all the files involved;

https://paste.pythondiscord.com/6LGQ

Thanks

[jaunty crow]

first checking for some obvious reasons why this could be, but those seems fine, continuing the search

@analog aurora i think one of the most important files might be api/calibration_data.py that isn't included

as that one contains the class that might be the one that is acting up

[analog aurora]

it's at the bottom

[jaunty crow]

oh, now i see it, their wasn't much code in that file (or class for that matter)

@analog aurora probably not the issue, but i see a lot of function calls like

calibrate_and_export(self, data, override_swatches)
```and
```py
return generate_preview(self, data)
```from within the class
don't you mean to call them as
```py
self.calibrate_and_export(data, override_swatches)
```and
```py
return self.generate_preview(data)
```instead?

[analog aurora]

Now this is giving me both a None exception, but it's also printing the supposedly None data??

data = self.all_calibration.image_list[0].calibration_data
print(data)

<api.calibration_data.CalibrationData object at 0x0000023098FD2120>
ERROR:root:'NoneType' object has no attribute 'calibration_data'

[analog aurora]

those those are from api.processor, not from within the Image class

[jaunty crow]

oh, now i saw the imports, okay
just that those functions had the exact same name as methods of the class that they were called from that was quite confusing

[analog aurora]

I guess I'll try to find another way of getting a reference to that CalibrationData, it should be the same for all images

This might be my new personal record on the weirdest bug I've found so far

Thanks for the help

[jaunty crow]

just a small note, the correct way of doing

self.global_target_image != None
```is
```py
self.global_target_image is not None

[jaunty crow]

by the way, where in your code did you put these debugging print statements?

[analog aurora]

Those were on def get_target_calibration_data(self) from Image

[jaunty crow]

was just asking as i didn't see it in the code you posted, not even commented out

@analog aurora this doesn't really check out (but should work anyways as it's "just" a type hinting "issue")

data: CalibrationData = None
```should probably be written as
```py
data: CalibrationData | None = None
```if it's allowed to ever be `None` (if it's an optional field)

you could skip it all together and just do

data = self.global_target_image.calibration_data
```or even
```py
data: CalibrationData = self.global_target_image.calibration_data
```if you want to type hint that variable there to something stricter then what `self.global_target_image.calibration_data` is defined as

@analog aurora this above is really also a potential issue with all of the attributes in your classes that you type hint and then initialize to None without including | None in the type hint

[analog aurora]

you mean not explicitly type-hinting that a variable can also be None could be the issue?

[jaunty crow]

i don't think it's the issue that you are experiencing here, but it is a potential issue in general

if you run a tool such as ty or pyright it will complain about this code

another tool that can be good to use is ruff and using ruff check --diff and ruff format --diff on your file to spot potential bugs and issues with your code (and also automatically reformat the code to follow some standards if you leave out the --diff flag)

[analog aurora]

Thanks I'll take a look at these

[jaunty crow]

but i still haven't found the source of your particular issue, it's a tricky one
probably "obvious" as soon as you find it, but until then it's not as "obvious"

@analog aurora if you don't want to initialize a variable in __init__ to anything other then None you could just have it as a attribute on the class with type hinting that doesn't allow for None, in that case it's "allowed", since the attribute doesn't come into existence for that class instance until that attribute is assigned to the first time (and all assignments must be of that type then)

might be able to catch the bug that way, but getting an error about trying to access a attribute before it has been assigned to
either that or add | None to the type hint so that you make it optional and can contain None

[analog aurora]

I'll try fixing the type hinting and see if that causes it to work, thanks

[jaunty crow]

i don't think it will make it magically work (since type hints are just hints and nothing more)
but it might surface some underlaying bug if you run tools on the code to check for problems

[rose reef]

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