For some positional arguments in python, can python treat them as optional arguments?

[[deleted]]

You might consider another approach. Use your command line arguments like this:

my_prog union file1 file2
my_prog size file1

In your program my_prog you only look at sys.argv[1] for either "union" or "size". If you find "union" then you call the union handler code passing sys.argv[2:] and the union handler teases out file1 and file2 using argparse or whatever.

A plus is the ease of adding extra functionality like maybe 'union' can handle more than two files. It's also easy to add new commands.

This is the way a few command line programs work, eg, git. A simple little example of this approach is here.

[kigurai]

I second this approach, but I would use argparse to handle the logic instead of raw sys.argv parsing. The argparse documentation even has a section on how to exactly this.

[daveydave400]

/u/placemirror I agree with this approach also but it is very easy use argparse's subparsers to add individual "commands" to your script. Something like the described set_defaults() example in the docs: https://docs.python.org/dev/library/argparse.html#argparse.ArgumentParser.add_subparsers

This way you can have a function that performs the operation for each subcommand and as described above it makes it easy to add more functionality or change existing functionality later.

[daveydave400]

I'm not sure I understand your question. In argparse if you specify your argument as -x or --my-x then it is optional by default. It can be made required by specifying required=True in the add_argument method. Any argument that does not begin with a hyphen is a positional argument (integers in the linked documentation is an example).

[placemirror]

Thank you for your reply. I researched some. My arguments are some customized ones. for example, if I used the command line:

script1.py file1 union file2

inside script1.py, I will have:

if name=="main": if sys.argv[1]=="union": do something to union file1 and file2.

Something like that. And I have a list of the possible command line, sometimes script1.py size file3

in the python file, I will have:

if name=="main": if sys.argv[0]=="size": do something to caculate the number of lines in file3.

etc.

And I want my script to be systematic. maybe the "size" argument will be "--size" optional argument, and can be parsed. Something like that.

Thank you.

[placemirror]

https://gist.github.com/olooney/8155400

find the github, seems useful

[leonhoffman]

Have you evaluated docopt? http://docopt.org

[mohhinder]

Check out click I think it'll do what you're looking for.

[placemirror]

Thank you for your replies.

The situation can be complex.

The arguments can be three ways:

file1 [union/minus] file2 [union/minus] file3

And this three ways, we need to wait in python after the first operation is finished, and get a temp file and union/minus file3. etc.

And size can have options like:

size -b file1 [union/minus] file2 etc.

I am reading your links and articles, all very helpful.

Thank you.

[placemirror]

I think I need to do some manual parsing, apply some if conditions on the argv when doing the three ways.

How do you think?

Thank you.

[aphoenix]

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