Can sys.argv handle optional arguments?

Question

from sys import argv
script, lira_cbt, [eur_hedge] = argv

if eur_hedge == None:
    #Do x
else:
    #Do y

I want it to be able to run with just lira_cbt as an argument (doing x), or with both lira_cbt and eur_hedge (doing y). Can this be achieved with sys.argv?

If your CLI gets that complex, you should probably start using `argparse` (or `optparse` if you're stuck with some older version). — , Feb 25 '12 at 10:01

varunl · Accepted Answer · 2015-10-10T16:38:56.173

31

Just use the length of sys.argv

if len(sys.argv) == 2:
  # do X
else:
  # do Y

edited Oct 10 '15 at 16:38

answered Feb 25 '12 at 08:01

varunl

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Can this be done if the length of `sys.argv` is only ever going to be 0 or 1? – Evan Oct 09 '19 at 02:10

score 8 · Answer 2 · answered Feb 25 '12 at 09:00

If this is to be part of more than a throw-away script, consider using argparse http://docs.python.org/library/argparse.html

At the moment it will be much more complicated, but it will help you keep documented the options your program accepts and also provide useful error messages unlike a "too many values to unpack" that the user might not understand.

score 3 · Answer 3 · answered Feb 25 '12 at 08:44

3

Another option is to extract the values from the argv list using try:

lira_cbt = sys.argv[1]
try:
  eur_hedge = sys.argv[2]
except IndexError:
  eur_hedge = None

if eur_hedge == None:
    # Do X
else:
    # Do Y

You could also take a look at getopt for a more flexible parser of command line arguments.

answered Feb 25 '12 at 08:44

Paul Hiemstra

59,984
12
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149

2

optparse or argparse would be much better than getopt! – carl Feb 25 '12 at 08:46

score 2 · Answer 4 · answered Feb 25 '12 at 07:55

2

You can simply check the length of sys.argv.

if len(sys.argv) < 2:
    # Error, not enough arguments

lira_cbt = sys.argv[1]
if len(sys.argv) == 2:
    # Do X
else:
    eur_hedge = sys.argv[2]
    # Do Y

answered Feb 25 '12 at 07:55

Lukáš Lalinský

40,587
6
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126

But no way to specifically pull the value in eur_hedge without throwing up a need more/too many variable to unpack argument? – Felix Feb 25 '12 at 07:58
2

No, there is no way to do it, unless you want to convert it to a function call and use something like `def main(script, lira_cbt, eur_hedge=None)` and `main(*sys.argv)`, which I definitely wouldn't do. – Lukáš Lalinský Feb 25 '12 at 08:00

score 0 · Answer 5 · answered Dec 15 '17 at 23:28

0

If I may suggest an alternative approach:

from sys import argv
option_handle_list = ['--script', '--lira_cbt', '--eur_hedge']
options = {}
for option_handle in option_handle_list:
    options[option_handle[2:]] = argv[argv.index(option_handle) + 1] if option_handle in argv else None
if options['eur_hedge'] == None:
    #Do x
else:
    #Do y

answered Dec 15 '17 at 23:28

satyakam shashwat

82
3

While this may work, using a module like `argparse` for this task would be both easier and more pythonic. – YSelf Dec 15 '17 at 23:39
@YSelf I am not debating on the easier / more traditional solution. Just answering the original question. – satyakam shashwat Dec 16 '17 at 19:07

score 0 · Answer 6 · answered Jun 27 '22 at 18:17

Here is a simple example that tries to read the argv1 input but does something else if one isn't provided.

from sys import argv

try:
    x = argv[1]
    print("x" + " Was given as an argument")
except:
    print("No Input Provided")

Console Output

Can sys.argv handle optional arguments?

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