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empty lines at end of file trimmed even with fmt: off #496
Description
Operating system: Linux Mint
Python version: 3.6.6
Black version: latest
Does also happen on master: yes
The following file:
# fmt: off
print("hello")
gets trimmed to:
# fmt: off
print("hello")
IOW, if the file ends with empty lines, they are removed.
Activity
zsol commentedon Sep 7, 2018
Sounds like a bug. Want to take a look at fixing it?
scolby33 commentedon Dec 17, 2018
The problem here appears to happen in
convert_one_fmt_off_pair, where the node enters as# fmt: off\n\nprint("hello")\n\nand exits as# fmt: off\n\nprint("hello")\n. I am continuing to investigate.scolby33 commentedon Dec 17, 2018
The function
generate_ignored_nodescreates a list of nodes that is just# fmt: off\n\nprint("hello")\n. This is where the final newline is lost.Unfortunately, I've reached the end of my experience/time to look at this today. I hope this has given someone more versed in the project a better starting place for fixing this bug.
EDIT: also, because of how test files are read in
read_dataintest_black.py, it will be difficult to write a test for this since the final\nwill be removed.felix-hilden commentedon Jan 29, 2022
At least our documentation states that
fmt: offshould be followed by afmt: on, but supporting a single off switch is a reasonable request.tagadearpit commentedon Aug 21, 2026
I reproduced this on the current development branch (26.5.2.dev98+g8947c48ef, CPython 3.12.3).
Minimal input:
Running black file.py removes the final blank line and produces:
The issue is that the parser stores trailing blank lines after the final statement in the END marker prefix, while fmt-off conversion currently discards that prefix. I have a focused fix that preserves the END marker prefix for an unclosed # fmt: off block at EOF, together with a regression test through Black’s file-formatting path.
Preserve trailing blank lines at EOF in unclosed fmt: off blocks (psf…
Preserve trailing blank lines at EOF in unclosed fmt: off blocks (#496)…
Preserve trailing blank lines at EOF in unclosed fmt: off blocks (psf…