title: ZipFile.testzip() returning different results on Python 2 and Python 3
body: <p>Using the <code>zipfile</code> module to unzip a large data file in Python works correctly on Python 2 but produces the following error on Python 3.6.0:</p>
  
  <p><code>BadZipFile: Bad CRC-32 for file 'myfile.csv'</code></p>
  
  <p>I traced this to error handling code checking the CRC values.</p>
  
  <p>Using <code>ZipFile.testzip()</code> on Python 2 returns nothing (all files are fine). Running it on Python 3 returns <code>'myfile.csv'</code> indicating a problem with that file.</p>
  
  <p>Code to reproduce on both Python 2 and Python 3 (involves a 300 MB download, sorry):</p>
  
  <pre><code>import zipfile
  import urllib
  import sys
  
  url = "https://de.iplantcollaborative.org/anon-files//iplant/home/shared/commons_repo/curated/Vertnet_Amphibia_Sep2016/VertNet_Amphibia_Sept2016.zip"
  
  if sys.version_info &gt;= (3, 0, 0):
      urllib.request.urlretrieve(url, "vertnet_latest_amphibians.zip")
  else:
      urllib.urlretrieve(url, "vertnet_latest_amphibians.zip")
  
  archive = zipfile.ZipFile("vertnet_latest_amphibians.zip")
  archive.testzip()
  </code></pre>
  
  <p>Does anyone understand why this difference exists and if there's a way to get Python 3 to properly extract the file using:</p>
  
  <pre><code>archive.extract("vertnet_latest_amphibians.csv")
  </code></pre>