@tirkarthi: Do you want to review this change?

@vstinner Change looks good to me.

While reviewing this PR seems like a similar change is also done at least for stdout in #7865 at https://github.com/python/cpython/pull/7865/files#diff-e94945dd18482591faf1e294b029a6afR25 . It assigns '-' by default and replaces '-' with sys.stdout at https://github.com/python/cpython/pull/7865/files#diff-e94945dd18482591faf1e294b029a6afR46 or file given in the command line.

This PR looks simpler than PR #7865.

@csabella: Hum, maybe wait until a consensus is found with PR #7865. This PR is correct, but I'm not sure if the other one is needed or not (it's a new feature). This PR is more a straightforward cleanup.

Sorry, I forgot to mention the #7865 was a feature. I have subscribed to the other and since I noticed it I wanted to convey this change might require changes and rebase in #7865 since it currently uses '-' as default to detect sys.stdout

Hi, I think #7865 is a bugfix and not a new feature and this PR does not fix the link bpo issue as far as I can tell

Hi @4383, can you clarify how is this related to the linked b.p.o report?

@remilapeyre @vstinner mine isn't a bpo or a fix or something like that.
It's just a minor update to avoid to check if stdin|stdout are needed, that's all.

But mine can help to a little bit to reduce the code complexity on #7865 by avoiding to check outfile=="-" and passing default value as a sys.stdout.

Ok, thanks for the clarification!

There is an issue to use two FileType arguments though, they open the file when parsing command line arguments (https://github.com/python/cpython/blob/master/Lib/argparse.py#L1198).

This means that when infile and outfile refer to the same file, it will get open for writing before you read from it and its content will be lost before the program even begin:

➜  ~ echo foo >test.txt
➜  ~ python3
Python 3.7.2 (default, Jan 13 2019, 12:50:01)
[Clang 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> open('test.txt')
<_io.TextIOWrapper name='test.txt' mode='r' encoding='UTF-8'>
>>> open('test.txt', 'w')
<_io.TextIOWrapper name='test.txt' mode='w' encoding='UTF-8'>
>>>
➜  ~ cat test.txt
➜  ~

I think it's not possible to use two argparse.FileType to solve the bug #33927. If we don't use FileType as the type of the infile argument, making it default to sys.stdout would not make much sense.

@remilapeyre yeah good point argparse.FileType on outfile is an issue. But default value can keep sys.stdout and you just have to check if type is <class '_io.TextIOWrapper'> instead check if value is equal to -.

I guess is a little bit more proper to assume that the default value is the sys.stdout instead check for string who are not really formalized anyway.

Thoughts?

With an <class '_io.TextIOWrapper'> object as the default value you are really sure that user want to display output directly on stdout`

@remilapeyre And you can continue your fix by removing argparse.FileType as a type on outfile and maybe use type as str.

Cf. my comments on yours #7865

I have made the requested changes; please review again

Thanks for making the requested changes!

@vstinner: please review the changes made to this pull request.

Thanks, I merged your PR.