I apologize if this question has been answered elsewhere but I have been unsuccessful in finding a satisfactory answer here or elsewhere.
I am somewhat new to python
pd.read_html returns you a list with one element and that element is the pandas dataframe, i.e.
df = pd.read_html(url) ###<-- List
df[0] ###<-- Pandas DataFrame
From http://pandas.pydata.org/pandas-docs/version/0.17.1/io.html#io-read-html, "read_html returns a list of DataFrame objects, even if there is only a single table contained in the HTML content".
So df = df[0].dropna(axis=0, thresh=4)
should do what you want.