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A follow up from a question I asked yesterday that allowed me to identify a new problem (How wonderful!). So I have this code that is converting a .dat file from (34354435.0000007, 623894584.000006) to 34354435.0000007, 623894584.000006 with .strip('()\n') and then removing a trailing newline with .rstrip('\n') so I can import it to matplotlib and plot a polygon. The order in the code is the other way around, but I don't think it matters as this brings up the same error regardless of where it is in the for loop;

lang=js
data_easting=[]
data_northing=[]

#Open the poly.dat file (in Python)
Poly = open('poly.dat','r')

#Loop over each line of poly.dat.
for line in Poly.readlines():
    line  = line.rstrip('\n')
    print (line +'_becomes')
    line  = line.strip('()\n')
    print (line)
    x,y = line.split(', ')
    data_easting.append(x)
    data_northing.append(y)
    
import numpy
data_easting = numpy.array(Easting,dtype=float)
data_northing = numpy.array(Northing,dtype=float)

from matplotlib import pyplot

I get a Value Error;

     16     line  = line.strip('()\n')
     17     print (line)
---> 18     x,y = line.split(', ')
     19     data_easting.append(x)
     20     data_northing.append(y)

ValueError: not enough values to unpack (expected 2, got 1)

And through the print function I've figured out it's trying to loop through the newline at the bottom (so when I try to split the data across x and y, it fails at the newline because the newline only has 1 value with no ", " defined in it.

...
(331222.6210000003, 672917.1531000007)_becomes
331222.6210000003, 672917.1531000007
_becomes

-----------------------------------------------

Isn't .rstrip supposed to remove the trailing newlines? I've also tried .replace, and including \r and in the rstrip function and I get the same result. What is wrong with my code that it won't respond to the .rstrip and .strip?

Alternatively, if there's a way to outright skip or stop the loop at the final data entry, that would bypass the problem I think.

Thanks,

A constricted learner.

Needs_Caffeine
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    Is there a blank line at the end of the file? – Ry- Nov 01 '20 at 15:17
  • Yep, I looked through it with notepad++ searching for anything that the code was missing and the last line is a whitespace (found by using ctrl-f and searching '\n'). When I try to to remove it with `.rstrip()`, `rstrip(' ')`, or `rstrip('\n')` , the same `Value Error` still comes up. – Needs_Caffeine Nov 01 '20 at 15:23
  • The `strip` indeed removes the `'\n'`, but now your `line` is just an empty string - `''`. So you're basically trying to do `x, y = ''.split(', ')` which will give the exact same error... – Tomerikoo Nov 01 '20 at 15:33
  • On topic: have a look at [How to read a file without newlines?](https://stackoverflow.com/q/12330522/10197418). Related: in your code sample, you open a file object but you never `close()` it. better use the [with](https://stackoverflow.com/q/1369526/10197418) statement. – FObersteiner Nov 01 '20 at 15:40
  • Thank you Tomerikoo and Mr Fuppes, you both have explained what was going wrong, and what I can do better with my code. I'll use that link to brush up! – Needs_Caffeine Nov 01 '20 at 15:59

1 Answers1

2

  • Remove the extra blank line from the end of the file.

  • If extra blank lines are to be expected in the input, you’ll need to detect and ignore them:

    for line in Poly:
    if line == '\n':
        continue

    ...
Ry-
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