How to add support of multi-line arguments for Python scripts using argparse?

Question

I've just created a Python project that uses argparse for parsing arguments. But it seems that it does not support multi-line arguments. One can check the example/command-line.sh in the project, and will find it does not understand the following style

#!/bin/bash
../scripts_gen.py --template template.txt \
                  --save-to scripts \
                  --param "{'data':'datasets.txt', \
                            'lambda':[`echo 0.{0..9}|sed -E 's/\s+/,/g'`], \
                            'seed':[233,874]}" \
                  --format "{data}_lambda={lambda}_seed={seed}.sh" \
                  --delete

Note that this is legal in shell script: one can always write

$ ls -l \
> -f

in console or shell script file (no prompt in this case). So can I add support for this via argparse? Thank you.

This should be OK. What error do you see? You might not need the `` within your quoted string. — SethMMorton
– SethMMorton, Commented Jun 7, 2013 at 20:13
@SethMMorton In the above example, I will see the Python script can recognize the first argument --template but ignoring the rest. Then the shell later complains that it cannot find commands like --save-to etc.. — Ziyuan
– Ziyuan, Commented Jun 7, 2013 at 20:15
The problem is in your bash script. If it worked as intended, python wouldn't even know there's a newline between arguments--the shell handles that and removes the newline. Most likely there's a space after the first backslash. — alexis
– alexis, Commented Jun 7, 2013 at 22:30
@alexis I was using Cygwin but later tried Debian 7.0 and it seems OK. It might be a problem of Cygwin. But Cygwin can recognize the ls example, so it's still a little weird. — Ziyuan
– Ziyuan, Commented Jun 8, 2013 at 9:42
Ok, if the same file works properly on Debian, then it's not a space after the backslash. Perhaps it's a problem with the line endings in your script? — alexis
– alexis, Commented Jun 8, 2013 at 17:17

alexis · Accepted Answer · 2013-06-08 22:34:32Z

Post-facto answer, based on my comments:

The problem is in your bash script. If it worked as intended, python wouldn't even know there's a newline between arguments--the shell handles that and removes the newline. Most likely there's a space after the first backslash.
But since the same file works properly on Debian but fails under cygwin, it was not a space after the backslash. Perhaps it's a problem with the line endings in your script?
So, the problem was automatic CR/LF conversion by git, combined with a strange refusal by cygwin to understand the line-ending conventions of its host operating system. Though you fixed it by hand-converting the script back to unix line endings, I would recommend a more robust solution: You could enable CR/LF support in cygwin (since you imply that it is an option), but my preference would be to also disable git's CR/LF mapping. And check that all your common tools and editors are configured to handle both kinds of line ending properly.

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