title: Why "os.sep" is faster than "os.path.join()"?
body: <p>I usually use "os.path.join()" when I connect path,I rarely use "os.sep".
  But I found "os.sep" is faster than "os.path.join()".Why?</p>
  
  <p><strong>My test code:</strong></p>
  
  <pre><code>import os
  import time
  
  a = 'E:\\video'
  b = 'image'
  c = '0001.jpg'
  start = time.clock()
  d = os.path.join(a,b,c)
  end = time.clock()
  print("%f " % (end - start)) #0.000011
  print(d) #E:\video\image\0001.jpg
  start = time.clock()
  e = a+os.sep+b+os.sep+c
  end = time.clock()
  print("%f " % (end - start)) #0.000001 
  print(e) #E:\video\image\0001.jpg
  </code></pre>
  
  <p><strong>Result:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/FTv0W.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FTv0W.jpg" alt="enter image description here"></a></p>