title: Dask Dataframe error: 'Future' object has no attribute 'drop'
body: <p>I am new with Dask. I have created a dask dataframe, dropped some columns using the drop command. After this I am performing additional operations. When I call compute,  get error: 'Future' object has no attribute 'drop'. </p>
  
  <p>Calling compute() immediately after the drop command works fine but when I call it few statements after, it gives me this error. Please suggest what is wrong here.</p>
  
  <p>By the way, I am using dask distributed on my local machine and version is 1.2.1.</p>
  
  <pre><code>import dask.dataframe as dd  
  from dask.distributed import Client  
  client = Client()   
  df = dd.read_csv("XYZ.csv", sep="\t",low_memory=False) #Its about 3 GB in size   
  df = df.persist() #Data is split ito 47 partitions   
  
  list_of_columns_to_delete = ['ABC', 'AXY', 'JDR']    
  
  df = df.drop(list_of_columns_to_delete, axis=1, errors=True)   
  
  df.EngineSpeed.mean().compute() #this works fine and computes the mean   
  df = df[(df.Time &lt; "23:59:59") ]   
  df = df[df.EngineSpeed &gt; 605]   
  df = df[df.ServiceBrakeCircuit1AirPressure.notnull()]   
  df = df[df.ServiceBrakeCircuit2AirPressure.notnull()]   
  df.GpsSpeed = df.GpsSpeed.where(df.GpsSpeed &lt; 111,111)    
  df.GpsSpeed.mean().compute() #This gives 'Future' object has no attribute 'drop' error`     
  </code></pre>
  
  <p>Kindly suggest what the error means and how it can be corrected.</p>