Saad Javed wrote:
> Hi,
>
> #!/usr/bin/env python
>
> import sys
>
> x = 'Saad is a boy'
>
> def main(x):
> a = []
> b = x.split(' ')
> for item in b:
> a.append(item)
> print a
> if __name__ == '__main__':
> x = sys.argv[1]
> main(x)
>
>
> How can I make this program run with the default value of x if I don't
> specify an argument at the command line?
> It should do this:
>
> saad@saad:~$ python test.py "Mariam is a girl"
> ['Mariam', 'is', 'a', 'girl']
>
> saad@saad:~$ python test.py
> ['Saad', 'is', 'a', 'boy']
>
> But the simply running "test.py" gives:
> Traceback (most recent call last):
> File "input_test.py", line 13, in <module>
> x = sys.argv[1]
> IndexError: list index out of range
>
>
> Saad
The argparse module (see <http://docs.python.org/2/library/argparse.html>)
offers a flexible way to specify command line arguments. Your program would
look like this:
$ cat optional_arg.py
#!/usr/bin/env python
import argparse
def main():
parser = argparse.ArgumentParser(
description="Print a sentence as a list of words")
parser.add_argument(
"sentence", nargs="?",
default="Mary had a little lamb")
args = parser.parse_args()
words = args.sentence.split()
print words
if __name__ == "__main__":
main()
...and work like this:
$ ./optional_arg.py
['Mary', 'had', 'a', 'little', 'lamb']
$ ./optional_arg.py "That's all folks"
["That's", 'all', 'folks']
It would include help...
$ ./optional_arg.py -h
usage: optional_arg.py [-h] [sentence]
Print a sentence as a list of words
positional arguments:
sentence
optional arguments:
-h, --help show this help message and exit
...and basic error reporting:
$ ./optional_arg.py That\'s all folks
usage: optional_arg.py [-h] [sentence]
optional_arg.py: error: unrecognized arguments: all folks
almost for free. So even if you find argparse too complex right now keep in
mind that it exists until you are comfortable enough with Python to start
making use of more parts of its standard library.
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