title: Pandas Loop and Append Failure
body: <p>So I'm trying to send a datframe of VINs to the nhtsa open source api and get the information back.  The below works with replacing <code>df['vin']</code> with an actual vin.  However when adding the loop to my function and trying to append, the result is that I get a blank dataframe back instead of the information for the 12 or so VINs.  What am I doing wrong?</p>
  
  <p>Code below:</p>
  
  <pre><code>import pandas as pd
  import requests
      #develop the data
  z = pd.DataFrame(columns = ["vin"], data = ['LHJLC79U58B001633','SZC84294845693987','LFGTCKPA665700387','L8YTCKPV49Y010001',
                                                   'LJ4TCBPV27Y010217','LFGTCKPM481006270','LFGTCKPM581004253','LTBPN8J00DC003107',
                                                   '1A9LPEER3FC596536','1A9LREAR5FC596814','1A9LKEER2GC596611','1A9L0EAH9C596099',
                                                   '22A000018'])
  
  z['manufacturer'] = ['A','A','A','A','B','B','B','B','B','C','C','D','D']
  
  
  
  def nhtsa(df):
      '''
      sends VIN to NHTSA for data call
      '''
      for i in df:
          url = 'https://vpic.nhtsa.dot.gov/api/vehicles/DecodeVINValuesBatch/'
          post_fields = {'format': 'json', 'data': df['vin']};
          r = requests.post(url, data=post_fields);
          x = r.json()
          f = pd.DataFrame(x['Results'])
          g = f[['VIN','Make','Manufacturer','ManufacturerId','ManufacturerType', 'Model','ModelYear', 'ABS','VehicleType', 'BodyClass','DisplacementCC','ErrorCode', 'SuggestedVIN']]
          csv = pd.DataFrame()
          csv = csv.append(g, ignore_index = True)
          return csv
  
  nhtsa(z)
  </code></pre>