title: How to fix "'pandas.compat' has no attribute 'string_types'" error in python3
body: <p>I am watching <a href="https://youtu.be/NM8Ue4znLP8?t=219" rel="nofollow noreferrer">this</a> tutorial where I am trying to use <a href="https://addisonlynch.github.io/iexfinance/stable/configuration.html#output-formatting" rel="nofollow noreferrer">iexfinance</a> to get stock data. You have the option to choose the data type when requesting the data, I chose "pandas". When I run the built-in function I get an error that reads <code>AttributeError: module 'pandas.compat' has no attribute 'string_types'</code></p>
  
  <p>I am using python 3.7. I have uninstalled and reinstalled both iexfinance and pandas. I also created and IEX cloud account and passed in a secret key like the documentation states, but the same error. The tutorial doesn't mention any of these steps and its confusing why his works and mine isn't. </p>
  
  <p>I have tried to make the code simpler by following examples on the website: Even when running:</p>
  
  <pre><code>from iexfinance.stocks import Stock
  
  df = Stock("AAPL", output_format="pandas")
  
  print(df.get_quote().head())
  
  </code></pre>
  
  <p>The error persists</p>
  
  <p>The expected output is: </p>
  
  <pre><code>                      AAPL
  avgTotalVolume    30578248
  calculationPrice     close
  change               -0.58
  changePercent     -0.00298
  close               207.27
  </code></pre>
  
  <p>The output I am receiving is:</p>
  
  <pre><code>Traceback (most recent call last):
    File "app.py", line 18, in &lt;module&gt;
      df = Stock("AAPL", output_format="pandas")
    File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/iexfinance/stocks/base.py", line 45, in __init__
      self.symbols = list(map(lambda x: x.upper(), _handle_lists(symbols)))
    File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/iexfinance/utils/__init__.py", line 43, in _handle_lists
      if isinstance(l, (compat.string_types, int)):
  AttributeError: module 'pandas.compat' has no attribute 'string_types'
  </code></pre>