python argv question

[tdrusk]

i am new to using commandline arguments in python. i am a bit confused as to why my code doesn't work when i pass commandline arguments, but does work when i just create a list in program. for example



import sys
i = [4,2,5,3,-22,33]
for p in range(1,len(i)):
print "pass "+str(p)
for c in range(p,0,-1):
print '\t'+str(i[c-1])+' checked with '+str(i[c])
if(i[c]<i[c-1]):
print '\tswapped '+str(i[c])+' with '+str(i[c-1])
t=i[c-1]
i[c-1]=i[c]
i[c]=t
print '\t'+str(i)
print "done: " +str(i)
gives me the output

pass 1
4 checked with 2
swapped 2 with 4
[2, 4, 5, 3, -22, 33]
pass 2
4 checked with 5
[2, 4, 5, 3, -22, 33]
2 checked with 4
[2, 4, 5, 3, -22, 33]
pass 3
5 checked with 3
swapped 3 with 5
[2, 4, 3, 5, -22, 33]
4 checked with 3
swapped 3 with 4
[2, 3, 4, 5, -22, 33]
2 checked with 3
[2, 3, 4, 5, -22, 33]
pass 4
5 checked with -22
swapped -22 with 5
[2, 3, 4, -22, 5, 33]
4 checked with -22
swapped -22 with 4
[2, 3, -22, 4, 5, 33]
3 checked with -22
swapped -22 with 3
[2, -22, 3, 4, 5, 33]
2 checked with -22
swapped -22 with 2
[-22, 2, 3, 4, 5, 33]
pass 5
5 checked with 33
[-22, 2, 3, 4, 5, 33]
4 checked with 5
[-22, 2, 3, 4, 5, 33]
3 checked with 4
[-22, 2, 3, 4, 5, 33]
2 checked with 3
[-22, 2, 3, 4, 5, 33]
-22 checked with 2
[-22, 2, 3, 4, 5, 33]
done: [-22, 2, 3, 4, 5, 33]
which is perfectly correct
but when i use commandline arguments i get a different(wrong) answer

import sys
i=sys.argv[1:]
for p in range(1,len(i)):
print "pass "+str(p)
for c in range(p,0,-1):
print '\t'+str(i[c-1])+' checked with '+str(i[c])
if(i[c]<i[c-1]):
print '\tswapped '+str(i[c])+' with '+str(i[c-1])
t=i[c-1]
i[c-1]=i[c]
i[c]=t
print '\t'+str(i)
print "done: " +str(i)

python insertionsort.py 4 2 5 3 -22 33
pass 1
4 checked with 2
swapped 2 with 4
['2', '4', '5', '3', '-22', '33']
pass 2
4 checked with 5
['2', '4', '5', '3', '-22', '33']
2 checked with 4
['2', '4', '5', '3', '-22', '33']
pass 3
5 checked with 3
swapped 3 with 5
['2', '4', '3', '5', '-22', '33']
4 checked with 3
swapped 3 with 4
['2', '3', '4', '5', '-22', '33']
2 checked with 3
['2', '3', '4', '5', '-22', '33']
pass 4
5 checked with -22
swapped -22 with 5
['2', '3', '4', '-22', '5', '33']
4 checked with -22
swapped -22 with 4
['2', '3', '-22', '4', '5', '33']
3 checked with -22
swapped -22 with 3
['2', '-22', '3', '4', '5', '33']
2 checked with -22
swapped -22 with 2
['-22', '2', '3', '4', '5', '33']
pass 5
5 checked with 33
swapped 33 with 5
['-22', '2', '3', '4', '33', '5']
4 checked with 33
swapped 33 with 4
['-22', '2', '3', '33', '4', '5']
3 checked with 33
['-22', '2', '3', '33', '4', '5']
2 checked with 3
['-22', '2', '3', '33', '4', '5']
-22 checked with 2
['-22', '2', '3', '33', '4', '5']
done: ['-22', '2', '3', '33', '4', '5']

i have a feeling i am just overlooking something stupid, but any advice as to why this is happing would be much appreciated.:guitar:

[schauerlich]

When you make the list yourself, you're making a list of integers. When you're getting it from the command line, you're getting a list of strings. You have to convert the arguments to integers.


numbers = sys.argv[:]
for number in numbers:
try:
number = int(number)
except:
print "Input must be integers"

[tdrusk]

When you make the list yourself, you're making a list of integers. When you're getting it from the command line, you're getting a list of strings. You have to convert the arguments to integers.


numbers = sys.argv[:]
for number in numbers:
try:
number = int(number)
except:
print "Input must be integers"

your tip got me in the right direction. thanks!



import sys
i=sys.argv[1:]
for j in range(len(i)):
try:
i[j]=int(i[j])
except:
print "input must be int"
for p in range(1,len(i)):
print "pass "+str(p)
for c in range(p,0,-1):
print '\t'+str(i[c-1])+' checked with '+str(i[c])
if(i[c]<i[c-1]):
print '\tswapped '+str(i[c])+' with '+str(i[c-1])
t=i[c-1]
i[c-1]=i[c]
i[c]=t
print '\t'+str(i)
print "done: " +str(i)

gives me


pass 1
4 checked with 2
swapped 2 with 4
[2, 4, 5, 3, -22, 33]
pass 2
4 checked with 5
[2, 4, 5, 3, -22, 33]
2 checked with 4
[2, 4, 5, 3, -22, 33]
pass 3
5 checked with 3
swapped 3 with 5
[2, 4, 3, 5, -22, 33]
4 checked with 3
swapped 3 with 4
[2, 3, 4, 5, -22, 33]
2 checked with 3
[2, 3, 4, 5, -22, 33]
pass 4
5 checked with -22
swapped -22 with 5
[2, 3, 4, -22, 5, 33]
4 checked with -22
swapped -22 with 4
[2, 3, -22, 4, 5, 33]
3 checked with -22
swapped -22 with 3
[2, -22, 3, 4, 5, 33]
2 checked with -22
swapped -22 with 2
[-22, 2, 3, 4, 5, 33]
pass 5
5 checked with 33
[-22, 2, 3, 4, 5, 33]
4 checked with 5
[-22, 2, 3, 4, 5, 33]
3 checked with 4
[-22, 2, 3, 4, 5, 33]
2 checked with 3
[-22, 2, 3, 4, 5, 33]
-22 checked with 2
[-22, 2, 3, 4, 5, 33]
done: [-22, 2, 3, 4, 5, 33]

[nvteighen]

When you make the list yourself, you're making a list of integers. When you're getting it from the command line, you're getting a list of strings. You have to convert the arguments to integers.


numbers = sys.argv[:]
for number in numbers:
try:
number = int(number)
except:
print "Input must be integers"


A bit smaller and in functional programming fashion:


import sys

args = None # It's always good to initialize stuff... see below.
try:
args = map(int, sys.argv[1:])) # argv[0] is always a string, so skip it!
except ValueError:
print("All arguments required to be integers")
# args will be None here. This allows you to check later in code whether
# args is valid or not where needed instead of immediately quitting the
# application by default.