title: python3: delete the columns that the value of columns is a certain value
body: <p>The is a dataframe(df1) like the following:</p>
  
  <pre><code> eye_l   eye_r    nose       mouse       ear     eyebrow_l  eyebrow_r  ...
    34_35_a -1_-1_-1  45_66_b    45_64_a     78_87_a  -1_-1_-1   -1_-1_-1
    35_38_a -1_-1_-1  75_76_b    -1_-1_-1     38_79_a -1_-1_-1 -1_-1_-1
    64_43_a -1_-1_-1  85_66_b    65_45_a     87_45_a  -1_-1_-1  -1_-1_-1
     ....................................................................
  </code></pre>
  
  <p>I want to just delete the columns that all the value of a column is -1_-1_-1 (such as eye_r, eyebrow_1, eyebrow_r), and please notice that some columns may have a number (not all) of value is -1_-1_-1 will be kept.</p>
  
  <p>I know that there is code like:</p>
  
  <pre><code>df1. drop(['eye_r', 'eyebrow_l', 'eyebrow_r '], axis=1, inplace=True)
  </code></pre>
  
  <p>But all the value is -1_-1_-1 of columns is not just three, there may be 100, and also there is a number of dataframes like such kind of dataframe. I want to process this issue in common method.
  Thanks</p>