title: Boto3 Object put method loads 0 bytes
body: <p>The following loads an empty file to my s3 bucket. Why?</p>
  
  <pre><code>df = pd.DataFrame([[1,2,3],[324,34,25], [463,23,43]])
  out = df.to_csv(index=False) # unicode string (i'm in python 3)
  
  s3 = boto3.resource('s3')
  BUCKET = "MyBucketThatDefExistsAndIHaveAccessTo"
  bucket = s3.Bucket(BUCKET)
  obj = bucket.Object('TEST1')
  obj.put(df.to_csv(index=False)) # loads an empty file "TEST1" to my bucket.
  
  # I've also tried, but same result.
  obj.put(bytes(df.to_csv(index=False), 'utf8')) 
  </code></pre>