title: how to use sys.stdin.readline()?
body: <p>I am using the jupyter notebook now.
  When I try to run the code below, it doesn't work from the third line.</p>
  
  <blockquote>
    <p>Error message : "invalid literal for int() with base 10: ''.</p>
  </blockquote>
  
  <p>I can't find any problem at third line.
  I want to use sys module than input() to reduce the running time.</p>
  
  <pre><code>from sys import stdin
  qu=[]
  for _ in range(int(stdin.readline())):
      arr = stdin.readline().split()
      if arr[0] == 'push':
          qu.append(arr[1])
      elif arr[0] == 'pop':
          if qu: print(qu.pop(0))
          else: print(-1)
      elif arr[0] == 'size':
          print(len(qu))
      elif arr[0] == 'empty':
          print(1-int(bool(qu)))
      elif arr[0] == 'front':
          if qu: print(qu[0])
          else: print(-1)
      elif arr[0] == 'back':
          if qu: print(qu[-1])
          else: print(-1)
      else:
          pass
  </code></pre>
  
  <blockquote>
    <p>ValueError Traceback (most recent call last)
     in 
         1 from sys import stdin
         2 qu=[]
    ---->3 for _ in range(int(stdin.readline())):
         4     arr = stdin.readline().split()
        5     if arr[0] == 'push':</p>
    
    <p>ValueError: invalid literal for int() with base 10: ''</p>
  </blockquote>