python split string and pick substring

Question

I am having a lot of trouble with the list returned by the split function in python. I am probably being incredibly dense.

My python code is as follows

str = "XXX:YYY:ZZZ"
var+=1
ins = str.split(':')
print ins

When the script runs it returns the following result

['XXX','YYY','ZZZ']

What i am struggling to do is pull out the string contained the second string in the list. I would have thought the following code at the end of the python code would work.

print ins[1]

but when i run it i get the following error

IndexError: list index out of range

Any help would be much appreciated

full code

import time
ser = serial.Serial("COM3", 9600)
print ser
time.sleep(3)
print "Sending serial data"
var = 0
while var<=10:
    str = ser.readline()
    print str
    var+=1
    ins = str.split(':')
    print ins
    print ins[0]
    if (str.split(':')=='end\n'):
        break
if(ser.isOpen()):
    print "Serial connection is still open."
    ser.close();
    print "Serial connectionnow terminated."

This returns

Serial<id=0x2a7fc50, open=True>(port='COM3', baudrate=9600, bytesize=8, parity='N', stopbits=1, timeout=None, xonxoff=False, rtscts=False, dsrdtr=False)
Sending serial data
Program Initiated

['Program Initiated\n']
Program Initiated

0:addsd:1

['0', 'addsd', '1\n']
0
1:addsd:2

['1', 'addsd', '2\n']
1
2:end:2

['2', 'end', '2\n']
2

Works for me. Please post your exact code and exact error message (full traceback). — Sven Marnach
– Sven Marnach, Commented Mar 5, 2011 at 18:48
Works perfectly for me. There's code you're not showing us though, var has no purpose, for instance. (It should also have a more descriptive name). Without all the code we can't help you. — Chris Pfohl
– Chris Pfohl, Commented Mar 5, 2011 at 18:50
P.S. your comment says you want to pick the index of the result...care to elaborate on your title in the question? (Or change the title?) — Chris Pfohl
– Chris Pfohl, Commented Mar 5, 2011 at 18:51
@Sven Marnach The full code is a little more complicated as the string it is that i am trying to split is coming from an arduino mega via a comm port. The string appears to be working fine as i have done tests on it. full code will be added above — jklmuk
– jklmuk, Commented Mar 5, 2011 at 18:59
then ins[1] will not work for the first time through. You'll need to skip it. — Chris Pfohl
– Chris Pfohl, Commented Mar 5, 2011 at 19:19

Chris Pfohl · Accepted Answer · 2011-03-05 19:29:14Z

1

Your code will not work in instances where the input you're analyzing has a length <= 1.

Try checking for that and handling it in your code.

answered Mar 5, 2011 at 19:29

Chris Pfohl

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1 Comment

jklmuk Over a year ago

as you were the first one to pick out my rookie mistake i have accepted your answer. thanks again

Marlen T. B. · Accepted Answer · 2011-03-05 19:51:15Z

0

One of the lines you are reading probably has a two '\n' characters in a row. When that string is read with readlines() and then spit it has no [1] index only a [0] index.

What output do you get for the program:

import serial // Or is serial a builtin for the version of python you are using?
print repr(serial.Serial("COM3", 9600))

Thanks, Marlen

edited Mar 5, 2011 at 19:51

answered Mar 5, 2011 at 19:08

Marlen T. B.

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10 Comments

Marlen T. B. Over a year ago

@jklmuk I think there must be two '\n' characters in a row at some point.

jklmuk Over a year ago

output of print repr(ins) is: ['Program Initiated\n'] ['0', 'addsd', '1\n'] ['1', 'addsd', '2\n'] ['2', 'end', '2\n']

Marlen T. B. Over a year ago

@jklmuk readline only reads up to a newline('\n') character if your string was "xxx:\n\n:xxx:yyy" I think your code wouldn't work.

jklmuk Over a year ago

@ marlen t. b. output is 'P' 'r' 'o' 'g' 'r' 'a' 'm' ' ' 'I' 'n' 'i' 't' 'i' 'a' 't' 'e' 'd' '\n' '0' ':' 'a' 'd' 'd' 's' 'd' ':' '1' '\n' '1' ':' 'a' 'd' 'd' 's' 'd' ':' '2' '\n' '2' ':' 'e' 'n' 'd' ':' '2' '\n'

jklmuk Over a year ago

@marlen t. b. your updated answer is correct the first string being returned doesn't have and index 1 which was causing the problem thanks for you help

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