title: logical or on list of pandas masks
body: <p>I have a list of boolean masks obtained by applying different search criteria to a dataframe. Here is an example list containing 4 masks: </p>
  
  <pre><code>mask_list = [mask1, mask2, mask3, mask4]
  </code></pre>
  
  <p>I would like to find the logical or of all of the masks in the list. In other words, </p>
  
  <pre><code>or_mask = mask_list[0] | mask_list[1] | mask_list[2] | mask_list[3]
  </code></pre>
  
  <p>Is there a compact way to accomplish this for a list containing an arbitrary number of masks? I understand that I can write a for loop as below, but is there a shorter, more pythonic way to do this?</p>
  
  <pre><code>for i in range(len(mask_list)):
      if i == 0:
          temp_mask_or = mask_list[i]
      else:
          temp_mask_or = temp_mask_or | mask_list[i]
  </code></pre>