Possible improvement to add_columns

[Hibbins]

Hello,

While building a table using add_columns I encountered issues when I wanted to use get_cell. I started debugging since I couldn't understand what it was, then I found that all the column keys had the value None**. This surprised me a bit since the docs said that column_key will be automatically generated if none were provided, however I have later understood this to simply be a misunderstanding others have encountered as well.

The issue with this becomes apparent when you then try to use other built-in functions such as in my case get_cell. You have to provide the row key and the column key. But if all the column keys are identical, it is impossible to get a particular cell value. In the docs the description of a ColumnKey is "Uniquely identifies a column in the DataTable." and I have a hard time understanding how setting all the keys to "None" would make them unique.

The solution for now has been to simply use add_column for every column I want to have in the table. However it would be smoother to be able to use add_columns for purposes like this.

My suggestion would be on of the following:

1. Let the user also input column key values and not only labels
2. Actually add column keys that just is the same value as the label, so they are not all just "None"

Appreciate any comments, maybe I am missing something.

[edward-jazzhands]

That actually sounds like it might be a bug. Do you think you could produce a code snippet (MRE) that reproduces the issue?

[Hibbins]

Oh ok!

Sure no problem! The way I used the function was as follows.

def on_mount(self) -> None:
    self.add_columns("Name", "Country", "Bitrate", "Codec")

I then tried looking at the actual columns in the dict and got the following for all of them.

After that I really wanted to be sure, so I did the following.

def on_mount(self) -> None:
    column_keys = self.add_columns("Name", "Country", "Bitrate", "Codec")
    print(f"add_columns values: {[key.value for key in column_keys]}")

Which yielded this:

[Hibbins]

Per the documentation add_columns returns a list of column keys.

Which is why I am assuming that the list I am seeing in my print is a list of the column keys.

[TomJGooding]

In the docs the description of a ColumnKey is "Uniquely identifies a column in the DataTable." and I have a hard time understanding how setting all the keys to "None" would make them unique.

Just to clarify: the generated ColumnKey objects are unique. When a value is not provided, the keys are compared by the object id.

Here's a quick example to demonstrate:

from textual.app import App, ComposeResult
from textual.widgets import DataTable


class TableApp(App):
    def compose(self) -> ComposeResult:
        yield DataTable()

    def on_mount(self) -> None:
        table = self.query_one(DataTable)
        
        col_1_key = table.add_column("C1")
        col_2_key = table.add_column("C2")
        self.notify(f"{col_1_key == col_2_key = }")

        row_1_key = table.add_row("R1C1", "R1C2")
        row_2_key = table.add_row("R2C1", "R2C2")
        self.notify(f"{row_1_key == row_2_key = }")

        self.notify(f"{table.get_cell(row_1_key, col_1_key) = }")
        self.notify(f"{table.get_cell(row_2_key, col_2_key) = }")


if __name__ == "__main__":
    app = TableApp()
    app.run()

[Hibbins]

Yes, but I am using add_columns. Using add_column yields no issues, as there I can actually set the key manually. But when using add_columns the only reasonable way of actually getting the column data is to grab it from self.columns and that contains a dict of Column objects, not ColumnKey objects. If I snatch one of these objects from the dict, it gives me an error saying TypeError: unhashable type: 'Column'.

I am assuming because it isn't actually a ColumnKey object, but it might also be the case that not even such an object would suffice as currently the only way that works from my tests is to actually have a proper key and then pass that to the get_cell function. It would be nice to test, but I cannot manage to get a proper ColumnKey object from anywhere.

Please do let me know if you know how I can get such an object after creating the columns using add_columns.

EDIT:

I tried to grab a proper ColumnKey object from the result that add_columns returns. That does actually work, so you are correct there. However, I still cannot see any other way of obtaining that particular data, which means I have to save it to an instance variable myself. I would much rather just be able to get that data directly from the table every time I need it and not having to rely on saving that data myself at the point of column creation.

Another issue is also that I cannot get the cell data using the actual name of the column, but rather have to keep track of the indexes and since the ColumnKey objects are in an array the order is not always guaranteed, which poses yet another potential issue.

In my opinion the only proper solution here that makes sense would be to let the user actually set the key manually for the add_columns function as well. Seeing as it is really cumbersome to actually use the other functions otherwise and in some regards even impossible to guarantee that it will always yield the correct data.

[TomJGooding]

I realise add_columns doesn't have all the options that add_column does. I'm not disagreeing with you, rather just trying to explain how the ColumnKeys are unique even without a value.

[Hibbins]

I realise add_columns doesn't have all the options that add_column does. I'm not disagreeing with you, rather I just trying to explain how the ColumnKey are unique without a value.

Yes, I just made an edit to the comment, you are correct. However as can be seen in the edit, I think this suggestion should still be considered, as you also seem to agree with.

[TomJGooding]

I've always just assumed that add_columns was intended as a convenient method when you don't care about the keys (or other options provided by add_column). 🤷

[Hibbins]

I've always just assumed that add_columns was intended as a convenient method when you don't care about the keys (or other options provided by add_column). 🤷

Ah ok, yeah fair enough!

I just find that add_columns feels much cleaner to use, in almost every scenario. But I also understand if I am alone on that hill haha 😅

I already have a "solution" for it, that is also backwards compatible, therefore wouldn't be a breaking change. I'll open a PR when I get some time over and we can take it from there. Might not even be something anyone else is struggling with.

Thanks for all the comments! 🙏