python - Why does this code raise csv.Error?

Question

I'm trying to write out CSV using Python's built-in csv module.

import csv
import sys
writer = csv.writer(sys.stdout, delimiter="|", quoting=csv.QUOTE_NONE)
writer.writerow(['"foo', "bar"])

The output I expect is:

"foo|bar

However, I get this:

Error: need to escape, but no escapechar set

The documentation says:

When the current delimiter occurs in output data it is preceded by the current escapechar character. If escapechar is not set, the writer will raise Error if any characters that require escaping are encountered.

Now, the delimiter ('|', the pipe character) doesn't appear anywhere in the data. Why is the CSV writer trying to escape something?

Answer 1

Setting quoting=csv.QUOTE_NONE is not enough; you also need to set quotechar to an empty string:

>>> import sys
>>> import csv
>>> writer = csv.writer(sys.stdout, delimiter="|", quoting=csv.QUOTE_NONE, quotechar='')
>>> writer.writerow(['"foo', "bar"])
"foo|bar

Otherwise, csv.writer() will try to escape any existing quotechar characters, but it needs csv.escapechar to be set for that.