title: list() but 'str' object is not callable error in python
body: <p>I am working in python 2.7.3,and tried to read a csv file <code>PNG_Files_R.csv</code> containing the following information:</p>
  
  <pre><code>"Group","Sample","T0" \n
  "HereausCPC","61","sample06_1_T0-Subvolume-resample_scale-1_x.png"
  </code></pre>
  
  <p>I would like to read the file in each row cell by cell, except the first row. but I could never use list() to get the numbers of rows, it reports ''str' object is not callable'</p>
  
  <pre><code>import Image
  import os,csv
  path_working="/media/Research/TEST_Program/PNG_Files"
  path_now=os.getcwd() 
  os.chdir(path_working)
  csv_filename='PNG_Files_R.csv'
  f = open('PNG_Files_R.csv', 'rb')
  reader = csv.reader(f) 
  rows = list(csv.reader(f))
  lineNum = len(rows)
  for rowNum in range(1,lineNum):
      print rows[rowNum][0]
  </code></pre>
  
  <p>I restart python and then no error pops</p>
  
  <p>thanks a lot in advance!</p>