File creation error when passing output file to `COPY TO` as a param

[jgrg]

What happens?

Using a placeholder for the output file in a COPY TO statement fails if the file does not already exist. Since I get the same error via both Rust and Python, it might not belong in either duckdb-rs or duckdb-python.

(Is a function to SQL escape parameters available via the API?)

To Reproduce

This Python code with an output file name as a param:

import duckdb
conn = duckdb.connect()
inp = "input.ndjson"
out = "output.ndjson"
conn.execute("COPY (FROM read_json(?)) TO ? (FORMAT JSON)", [inp, out])

fails with:

    conn.execute("COPY (FROM read_json(?)) TO ? (FORMAT JSON)", [inp, out])
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_duckdb.IOException: IO Error: No files found that match the pattern "output.ndjson"

LINE 1: COPY (FROM read_json(?)) TO ? (FORMAT JSON)
                   ^

Whereas incorporating the file name into the string works, and tmp.ndjson is created:

safe = out.replace("'", "''")
conn.execute(f"COPY (FROM read_json(?)) TO '{safe}' (FORMAT JSON)", [inp])

It seems that having the output file as a placeholder almost works, but the fopen() mode is perhaps wrong.

OS:

MacOS

DuckDB Package Version:

1.5.0

Python Version:

3.13

Full Name:

James Gilbert

Affiliation:

Wellcome Sanger Institue

What is the latest build you tested with? If possible, we recommend testing with the latest nightly build.

I have tested with a stable release

Did you include all relevant data sets for reproducing the issue?

Not applicable - the reproduction does not require a data set

Did you include all code required to reproduce the issue?

• Yes, I have

Did you include all relevant configuration to reproduce the issue?

• Yes, I have