title: Dask dataframe read_csv error: Could not serialize object of type tuple
body: <p>Did not receive a resolution on the Dask Github page so asking here. </p>
  
  <p>Github issue link: <a href="https://github.com/dask/dask/issues/5156" rel="nofollow noreferrer">https://github.com/dask/dask/issues/5156</a></p>
  
  <p>The issue:</p>
  
  <p>Encountered the following error when reading this CSV (<a href="https://github.com/h2oai/h2o-tutorials/blob/master/tutorials/data/allyears2k.csv" rel="nofollow noreferrer">https://github.com/h2oai/h2o-tutorials/blob/master/tutorials/data/allyears2k.csv</a>):
  <strong>Code</strong>:</p>
  
  <pre><code>from dask.distributed import Client
  import dask.dataframe as dd
  client = Client()
  file = "allyears2k.csv"
  df = dd.read_csv(file, encoding='latin-1', blocksize=None)
  df.head()
  </code></pre>
  
  <p><strong>Error</strong>:</p>
  
  <p>TypeError: ('<strong>Could not serialize object of type tuple</strong>.', "(, (, (, , [.parser_f at 0x7f5e922f46a8>, (, , 0, None, b'\n'), b'Year,Month,DayofMonth,DayOfWeek,DepTime,CRSDepTime,ArrTime,CRSArrTime,UniqueCarrier,FlightNum,TailNum,ActualElapsedTime,CRSElapsedTime,AirTime,ArrDelay,DepDelay,Origin,Dest,Distance,........</p>
  
  <p>It works fine using the following Pandas code: </p>
  
  <pre><code>import pandas as pd
  datafile = "allyears2k.csv"
  df=pd.read_csv(datafile, encoding='latin-1', dtype='object')
  </code></pre>
  
  <p>Following are the version details:</p>
  
  <pre><code>Python 3
  Pandas 0.25.0
  OS:
  sh-4.2$ cat /etc/release
  NAME="Red Hat Enterprise Linux Server"
  VERSION="7.6 (Maipo)"
  ID="rhel"
  ID_LIKE="fedora"
  VARIANT="Server"
  
  dask and dask distributed: 
  2.1.0
  2.1.0
  </code></pre>
  
  <p>Adding screenshot of (the same) error even after specifying dtype=object.</p>
  
  <p><a href="https://i.stack.imgur.com/3eeuF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3eeuF.png" alt="enter image description here"></a></p>