Why does the following short script in Python disregard the condition in "if"?

Question

I want it to give 'Number of donuts: many' when the argument is more than 10 and 'Number of donuts: ' when the argument is count<10. But it always gives me 'Number of donuts: many'

#!/usr/bin/python2.6 -tt
import sys
def donuts(count):
  if count < 10:
    x = str(count)
  else:
    x = 'many'
  print 'Number of donuts: ' + x

def main():
  donuts(sys.argv[1])

if __name__ == "__main__":
  main()

See http://stackoverflow.com/questions/7969552/why-does-4-3-return-true-in-python-2 — agf, Apr 06 '12 at 20:58
Hint: What do you expect to happen when I run `donuts.py bananas`? Why? What actually does happen? — Karl Knechtel, Apr 06 '12 at 22:05

score 6 · Accepted Answer · answered Apr 06 '12 at 20:50

sys.argv will only contain strings, even if you provide integers as arguments, so for example if you called this as python donuts.py 4, then sys.argv[1] would be '4' and you would attempt the comparison '4' < 10 when you actually want 4 < 10.

So first, try to convert sys.argv[1] to an int:

def main():
    donuts(int(sys.argv[1]))

You may want to add some error handling as well, in case an argument is not provided or it is not an integer:

def main():
    try:
        donuts(int(sys.argv[1]))
    except IndexError:
        print 'Missing argument'
    except ValueError:
        print 'Invalid argument'

Thanks very much for the answer! It was very instructive for a new python user like me. — Nima Alidoust, Apr 09 '12 at 00:13

score 5 · Answer 2 · answered Apr 06 '12 at 20:50

5

count is a string. Try count = int(count)

answered Apr 06 '12 at 20:50

bluepnume

16,460
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Andbdrew · Answer 3 · 2012-04-08T23:21:16.473

3

You should convert count to an int before comparing it to 10:

#!/usr/bin/python2.6 -tt
import sys
def donuts(count):
    if int(count) < 10:
        x = count
    else:
        x = 'many'
    print 'Number of donuts: %s' % x

def main():
    donuts(sys.argv[1])

if __name__ == "__main__":
    main()

edited Apr 08 '12 at 23:21

answered Apr 06 '12 at 20:48

Andbdrew

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score 3 · Answer 4 · answered Apr 06 '12 at 20:50

3

Try converting the count parameter to an int for the comparison:

if int (count) < 10:
  x = str (count)
else:
  x = 'many'

Because you're passing in a string argument for the count parameter, the comparison is failing.

answered Apr 06 '12 at 20:50

scwagner

3,975
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score 3 · Answer 5 · answered Apr 06 '12 at 20:50

3

You don't take the input in as an integer to begin with.

Change:

def main():
  donuts(sys.argv[1])

to:

def main():
  donuts(int(sys.argv[1]))

You will run into an issue if they put in a string or decimal instead of a numerical value, though.

answered Apr 06 '12 at 20:50

Makoto

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Why does the following short script in Python disregard the condition in "if"?

5 Answers5