Problems with parsing when an option includes escapes Python does not like

[mdhall272]

MWE:

parser <- ArgumentParser(description='foo')
parser$add_argument('bar', default = "[\\D]")
parser$parse_args()

The error is:

Error in if (grepl("^\\{|^\\[", output)) { : the condition has length > 1

The reason is apparently that python is adding a warning string <stdin>:19: SyntaxWarning: invalid escape sequence '\\D' to output which causes an error at line 251 of argparse.R

[trevorld]

Can you provide me your sessionInfo() and python3 --version?

This doesn't seem to reproduce for me on Ubuntu 22.04.4 LTS with Python 3.10.12 in the bash shell

~/tmp$ cat argparse_bug.R 
library("argparse")
parser <- ArgumentParser(description='foo')
parser$add_argument('--bar', default = "[\\D]")
a <- parser$parse_args()
cat("bar: ", a$bar, "\n")
~/tmp$ Rscript argparse_bug.R 
bar:  [\D] 
~/tmp$ Rscript argparse_bug.R --bar=[\\D]
bar:  [\D] 

[mdhall272]

> sessionInfo()
R version 4.3.3 (2024-02-29)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Sonoma 14.3.1

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.11.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: Europe/London
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] argparse_2.2.2

loaded via a namespace (and not attached):
[1] compiler_4.3.3   R6_2.5.1         tools_4.3.3      findpython_1.0.8 jsonlite_1.8.8  

And presuming you use the vanilla findpython::find_python_cmd:

> find_python_cmd()
[1] "/opt/homebrew/bin/python3.12"

[trevorld]

• Okay, thanks for the extra info.
• I've compiled Python 3.12 locally and this issue reproduces with that version of Python.
• This issue does not seem to reproduce with Python 3.11 and lower.

[trevorld]

Looks like a new warning in Python 3.12:

~/tmp$ python3.11
Python 3.11.0rc1 (main, Aug 12 2022, 10:02:14) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> s = "\D"

~/tmp$ python3.12
Python 3.12.2 (main, Apr  2 2024, 07:10:36) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> s = "\D"
<stdin>:1: SyntaxWarning: invalid escape sequence '\D'

[trevorld]

Options seem to be:

1. Send to python as a "raw" string. This will probably escape all escape sequences even ones python recognizes. This may break code that relies on {argparse} passing in a recognized escape sequence to python.

2. Manually escape any unrecognized escape sequence with an extra \ but don't escape any recognized escape sequence that Python recognizes. This may be non-trivial to do. This seems to be a list of recognized escape characters: https://docs.python.org/3/reference/lexical_analysis.html#escape-sequences

3. Don't do either one but provide a more informative error message or warning.