I/O file not getting opened

问题:

I have this csv file dl.dropboxusercontent.com/s/tb4yc3lm3gg3j22/out.csv and I am trying to replace the last column with the read method below. In my input.csv i have to replace the last filed with some calculation. I trying as below but somehow i am getting ValueError: I/O operation on a closed file. Can you help me point out the mistake. As i am trying to open input file and write everything including the new value to out.csv file which doesnt exist initially but should be constructed on the fly.

def read():
    for file in os.listdir("./"):
        if file.endswith('.csv'):
            fNameFull = os.path.basename(file)
            inputFileName = os.path.splitext(file)[0]
            with open(fNameFull, "rb") as infile, open('out.csv', "wb") as outfile:
                r = csv.DictReader(infile)
                w = csv.DictWriter(outfile, r.fieldnames)
                w.writeheader()
                for row in r:
                    if not row["col_last"].strip():
                        row["col_last"] = "calc_value"
                    w.writerow(row)

if __name__ == '__main__':
    main()
    read()

Error:

Traceback (most recent call last):
  File "C:\Users\hp\Desktop\final\text\finalmod.py", line 50, in <module>
    read()
  File "C:\Users\hp\Desktop\final\text\finalmod.py", line 39, in read
    w.writeheader()
  File "C:\Python27\lib\csv.py", line 137, in writeheader
    self.writerow(header)
  File "C:\Python27\lib\csv.py", line 148, in writerow
    return self.writer.writerow(self._dict_to_list(rowdict))
ValueError: I/O operation on closed file