Python argparse: How to insert newline the help text in subparser?

Question

This question is related to a question asked earlier, but might be unrelated. Question is: How to use newlines in the help text in the given (working) example below, when using subparsers?

import argparse

parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter)

subparsers = parser.add_subparsers()

parser_start = subparsers.add_parser('stop')
parser_start.add_argument("file", help = "firstline\nnext line\nlast line")

print parser.parse_args()

My output is as follows:

tester.py  stop -h
usage: tester.py stop [-h] file

positional arguments:
  file        firstline next line last line

optional arguments:
  -h, --help  show this help message and exit

The expected output for the help on file should be:

first line
next line
last line

Answer 1

The subparsers.add_parser() method takes the same ArgumentParser constructor arguments as argparse.ArgumentParser(). So, to use the RawTextHelpFormatter for the subparser, you need to set the formatter_class explicitly when you add the subparser.

>>> import argparse
>>> parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter)
>>> subparsers = parser.add_subparsers()

Change this line to set the formatter_class of the subparser:

>>> parser_start = subparsers.add_parser('stop', formatter_class=argparse.RawTextHelpFormatter)

Now, your help text will contain the newlines:

>>> parser_start.add_argument("file", help="firstline\nnext line\nlast line")
_StoreAction(option_strings=[], dest='file', nargs=None, const=None, default=None, type=None, choices=None, help='firstline\nnext line\nlast line', metavar=None)

>>> print parser.parse_args(['stop', '--help'])
usage:  stop [-h] file

positional arguments:
  file        firstline
              next line
              last line

optional arguments:
  -h, --help  show this help message and exit