No output from show_graph from 0.14.11

[braaannigan]

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• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of Polars.

Issue description

In Jupyterlab I don't get any output from show_graph from version 0.14.11 onwards. Works fine with many versions before that.

Note: if I just output a LazyFrame (i.e. comment out show_graph in the example below) in version 0.14.11+ then I do get a graph with the unoptimised plan.

Reproducible example

pl.DataFrame(
    [{'VendorID': 'id1', 'pickup': '2022-01-01T00:04:14.000000'},
     {'VendorID': 'id2', 'pickup': '2022-01-01T00:32:17.000000'}]
).write_csv("sample.csv")
(
    pl.scan_csv("sample.csv",parse_dates = True)
    .filter(pl.col("VendorID") == 1)
    .show_graph()
)

Expected behavior

Expected to output a graph

Installed versions

---Version info---
Polars: 0.14.11
Index type: UInt32
Platform: Linux-5.10.104-linuxkit-x86_64-with-glibc2.28
Python: 3.10.1 (main, Dec 21 2021, 09:50:13) [GCC 8.3.0]
---Optional dependencies---
pyarrow: 10.0.0
pandas: 1.5.1
numpy: 1.23.4
fsspec: <not installed>
connectorx: 0.3.1
xlsx2csv: 0.8

[braaannigan]

More info:
in version 0.14.10 we get:

df = pl.DataFrame(
    [{'VendorID': 'id1', 'pickup': '2022-01-01T00:04:14.000000'},
     {'VendorID': 'id2', 'pickup': '2022-01-01T00:32:17.000000'}]
).lazy()
optimized = True
df._ldf.to_dot(optimized)
'graph  polars_query {\n"TABLE\nπ */2;\nσ -\n[(0, 0)]"\n}'

but in version 0.14.11 we get:

df = pl.DataFrame(
    [{'VendorID': 'id1', 'pickup': '2022-01-01T00:04:14.000000'},
     {'VendorID': 'id2', 'pickup': '2022-01-01T00:32:17.000000'}]
).lazy()
optimized = True
df._ldf.to_dot(optimized)
'graph  polars_query {\n\n\n}'

So it seems like the issue is in to_dot.

I'll keep looking into it

[braaannigan]

There were a few changes to to_dot between 8th (0.14.10) and 13th (0.14.11) September to the Rust code:
https://github.com/pola-rs/polars/commits/2b81197d6b7c0c82640d125b48142604b890d717/polars/polars-lazy/src/dot.rs

This is probably as far as I can take this at this point