Error in reading and writing CSV format file in python

[MRAB]

On 2013-02-11 12:44, inshu chauhan wrote:
>
> On Mon, Feb 11, 2013 at 1:26 PM, Steven D'Aprano
> <steve+comp.lang.python at pearwood.info
> <mailto:steve+comp.lang.python at pearwood.info>> wrote:
>
>     inshu chauhan wrote:
>
>      > In the programme below I am trying to read two csv format files and
>      > process them and write a new file with some of theirs data.
>      >
>      > import csv
>      > f1_reader = csv.reader(open(r"Z:\Weka
>      > work\Feature_Vectors_Fullset_00.arff"))
>      > f2_reader = csv.reader(open(r"Z:\Weka
>      > work\Feature_Vectors_Fullset_00_noxy+class.arff"))
>      > nf = open(r"Z:\Weka work\classified_image00_withoutxy.arff", "w")
>      >
>      > while True:
>      >     l1 = f1_reader.next()
>      >     while len(l1) != 12:
>      >         l1 = f1_reader.next()
>      >     l2 = f2_reader.next()
>      >     while len(l2) != 11:
>      >         l2 = f2_reader.next()
>      >
>      >     ix = l1[0].strip()
>      >     iy = l1[1].strip()
>      >     classification = l2[8].strip()
>      >
>      >     print >> nf, ix, iy, classification
>      >
>      > nf.close()
>      >
>      > This programme is giving me this error now :
>      >
>      > Traceback (most recent call last):
>      >   File "Z:\Weka work\final_image_classificationwithoutxy.py",
>     line 16, in
>      > <module>
>      >     l2 = f2_reader.next()
>      > StopIteration
>      >
>      >
>      > what could be a possible reason to StopIteration ???
>
>     next() raises StopIteration when there is nothing else to return.
>
>
>     py> it = iter([1, 2, 3])
>     py> it.next()
>     1
>     py> it.next()
>     2
>     py> it.next()
>     3
>     py> it.next()
>     Traceback (most recent call last):
>        File "<stdin>", line 1, in <module>
>     StopIteration
>
>
>     You have reached the end of the file and there is nothing else for
>     the CSV
>     reader to return, so it raises StopIteration.
>
>
>
> But why does it has nothing to return so early before traversing the
> whole file ? Is there any way it can be corrected ?  And also the
> programme isn't writing anything to the file ?
>
Try adding some logging so that you can see what it's doing. A simple way
would be something like:

log_file = open(r"Z:\Weka work\log.txt", "w")

...

l1 = f1_reader.next()
print >> log_file, "Read from f1:", l1
print >> log_file, "Length is", len(l1)
while len(l1) != 12:
     l1 = f1_reader.next()
     print >> log_file, "Read from f1:", l1
     print >> log_file, "Length is", len(l1)

and so on.