Minor improvements in CLI

[cknabs]

This PR adds the following (minor) improvements to the CLI:

• Removes the unreachable checks for domain and file_types, since this is already done by argparse
• Generalizes the checks for non-negative arguments
• Does not create and print the save_directory if download_files is False
• Allows to specify an output file for saving links when using -f with an argument. If only -f is specified, the links are saved to html_links_<TIMESTAMP>.txt, as before.

Thanks for the good work, really appreciate it!

[opsdisk]

Thanks for taking the time to submit a PR @cknabs! Please give me a few days to take a look.

[opsdisk]

Nice upgrade to the -f switch. I like it!

[opsdisk]

I've never seen this function convention before. It was hard to google for as well...is this called something specifically?

How is the actual value from argparse being passed? Are you overriding a .check() function within argparse or something?

I definitely like the spirit of this and want to keep it, but anyway it could be simplified? Or do you have some documentation recommending this for Python argparse type checking?

[cknabs]

The type argument of argparse's add_argument() is a callable that takes a string, converts it to the desired type, and can do some basic type-checking (see https://docs.python.org/3/library/argparse.html#type).

Here pos(T) returns such a callable (called check(), but the name has no special meaning) that maps a string to a result of type T. It might be simpler to define separate pos_float() and pos_int(), and then use type=pos_int instead of type=int:

def pos_int(value):
    try:
        value_int = int(value)
        assert value_int >= 0
        return value_int
    except (AssertionError, ValueError):
        raise argparse.ArgumentTypeError(f"invalid value '{value}', must be an int >= 0")

In this particular case, I think checking that these 3 args are positive after parsing is fine, a callable returning a callable / using custom "types" is a bit overkill for such a simple interface.
The improvement provided here is minimal, this kind of custom type is more useful and relevant for a larger number of arguments with similar constraints, which isn't really the case here.

Let me know what you'd prefer, and I can amend the PR :)

[opsdisk]

Learn something new every day! If you could make it two separate functions:

• positive_int()
• positive_float()

and keep the simple function check you have above instead of a callable returning a callable...that'd be perfect.

[cknabs]

Done, feel free to squash everything into one commit if you think that helps.
Thanks again for the good work, and for taking the time to look at the PR :)

[opsdisk]

Thanks for your contributions @cknabs!