如何知道第三个参数是否传递给脚本？

Question

I am working on a script that uses English words for their argument, not the traditional --argument or -a .

I have not dare to deal this with argparse, but when I do this with sys.argv like this:

if sys.argv[3]:
    print('yes, there is a third argument')

I get an IndexError: list index out of range . What is the possible way to tackle this? I want to know if there is third argument.

Answer 1

You want to check the length of argv :

if len(sys.argv) > 3:
    print('yes, there is a third argument')

If you have time, though, it's worth learning argparse. It's not too scary, and it makes your code much easier to read.

Answer 2

You can use len() to check the length first or catch the IndexError .

if len(sys.argv) > 3:
    # all three arguments are present
    print 'arg1', sys.argv[1], 'arg2', sys.argv[2], 'arg3', sys.argv[3]

or:

try:
   arg1, arg2, arg3 = sys.argv[1], sys.argv[2], sys.argv[3]
except IndexError:
   # arguments are missing