title: How do I enable the REFS_OK flag in nditer in numpy in Python 3.3?
body: <p>Does anyone know how one goes about enabling the REFS_OK flag in numpy? I cannot seem to find a clear explanation online. </p>
  
  <p>My code is:</p>
  
  <pre><code>import sys
  import string
  import numpy as np
  import pandas as pd
  SNP_df = pd.read_csv('SNPs.txt',sep='\t',index_col = None ,header = None,nrows = 101)
  output = open('100 SNPs.fa','a')
  for i in SNP_df:
      data = SNP_df[i]
      data = np.array(data)
      for j in np.nditer(data):
          if j == 0:
              output.write(("\n&gt;%s\n")%(str(data(j))))
          else:
              output.write(data(j))
  </code></pre>
  
  <p>I keep getting the error message: Iterator operand or requested dtype holds references, but the REFS_OK was not enabled.</p>
  
  <p>I cannot work out how to enable the REFS_OK flag so the program can continue...</p>