python3 List with .sort() goes wrong

Question

Im trying to sort a list in Python 3 using Visual Studio Code: I take my list from the arguments in the commandline. The first argument is ignored that's my needle variable. After adding all variables in the lost I want to sort the list. The problem is that it gets sorted in a rather strange way

after 2 comes 21 and then 3 after 5 comes 55 and than 6

This is my commandline:

C:\Users\Gebruikertje\Desktop\Python>python find.py 21 2 3 4 5 6 21 55 3

this is the output:

['2', '21', '3', '3', '4', '5', '55', '6']

This is the part of the code im referring to

import sys

finish = len(sys.argv)
needle = sys.argv[1]
haystack = []
for i in range (2,finish ):
    haystack.append(sys.argv[i])
haystack.sort()
print(haystack)

you are sorting a list of strings (not integers), try haystack.sort(key = lambda x: int(x)) or just make your list integers to begin with — Chris_Rands
– Chris_Rands, Commented Oct 6, 2017 at 11:49
This is because the numbers are strings. Try the same code with integers. — Eduardo
– Eduardo, Commented Oct 6, 2017 at 11:50
@JonClements Whoops yep agreed, but they probably actually don't want a list of strings initially — Chris_Rands
– Chris_Rands, Commented Oct 6, 2017 at 11:54

bhansa · Accepted Answer · 2017-10-06 11:59:34Z

2

You are trying to sort a list of strings.

Convert them to int while adding them to list.

haystack.append(int(sys.argv[i]))

You can also use map() here:

haystack = map(int, sys.argv[1:])

edited Oct 6, 2017 at 11:59

answered Oct 6, 2017 at 11:49

bhansa

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1 Comment

zorange Over a year ago

Thank you a lot. That was exactly the problem. One step forward in the world of Python

Mureinik · Accepted Answer · 2017-10-06 11:50:58Z

1

The values inputed from argv are strings, and thus are sorted lexicographically. You should convert them to numbers if you wan to sort them numerically. Doing this in a list comprehension could also help clean up some boiler plate from your loop:

haystack = [int(x) for x in sys.argv[1:]]
haystack.sort()

answered Oct 6, 2017 at 11:50

Mureinik

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Eduardo · Accepted Answer · 2017-10-06 11:53:50Z

1

Try:

x = ['2', '21', '3', '3', '4', '5', '55', '6']
y = [int(number) for number in x]
y.sort()

# Result = [2, 3, 3, 4, 5, 6, 21, 55]

answered Oct 6, 2017 at 11:53

Eduardo

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