specifying a list as a command line argument in python

Question

I am using getopt to process a command line optional argument, which should accept a list. Something like this:

foo.py --my_list=[1, 2, 3, 4,5]  

But this trims everything after "[1,"

My questions are: A) Is there a way to specify a list without converting it into a string? (using getopt)

B) If I am to convert the list into a string, how to convert this list to a string? e.g. something like mylist.split("?") to get rid of square brackets ?? is there a better way?

Thank you

Answer 1

There are two options that I can think of:

• Use optparse, and use append action to specify what you want to do as: foo.py --my_list=1 --my_list=2 ....
• Specify your commandline as foo.py --my_list='1,2,3,4,5', and then use x.split(',') to get your values in a list. You can use getopt or optparse for this method.

The advantage of the first method is that you can get integer values in the list directly, at the expense of the commandline being longer (but you can add a single-charecter option for --my_list if you want). The advantage of the second is shorter command line, but after the split(), you need to convert the string values '1', '2', etc., to integers (pretty easy as well).

Answer 2

If I can't use a standard parser (optparse or argparse) to my application then I use the ast.literal_eval function to parse input arguments of type list as follows:

import sys, ast  inputList = ast.literal_eval( sys.argv[1] ) print type( inputList ) print inputList 

Let suppose that this code is stored in testParser.py file. By executing the script:

$ python testParser.py  "[1,2,3,4, [123, 456, 789], 'asdasd']" 

we get the following output:

<type 'list'> [1, 2, 3, 4, [123, 456, 789], 'asdasd'] 

So, using the secure enough ast.literal_eval function and inserting the list as a string of code we have the desirable result.

Useful links:

Using python's eval() vs. ast.literal_eval()?

http://docs.python.org/2/library/functions.html?highlight=eval#eval