text: from __future__ import print_function
  # Time:  O(n)
  # Space: O(1)
  #
  # The API: int read4(char *buf) reads 4 characters at a time from a file.
  #
  # The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.
  #
  # By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.
  #
  # Note:
  # The read function will only be called once for each test case.
  #
  
  # The read4 API is already defined for you.
  # @param buf, a list of characters
  # @return an integer
  def read4(buf):
      global file_content
      i = 0
      while i < len(file_content) and i < 4:
          buf[i] = file_content[i]
          i += 1
  
      if len(file_content) > 4:
          file_content = file_content[4:]
      else:
          file_content = ""
      return i
  
  class Solution(object):
      def read(self, buf, n):
          """
          :type buf: Destination buffer (List[str])
          :type n: Maximum number of characters to read (int)
          :rtype: The number of characters read (int)
          """
          read_bytes = 0
          buffer = [''] * 4
          for i in xrange(n / 4 + 1):
              size = read4(buffer)
              if size:
                  buf[read_bytes:read_bytes+size] = buffer
                  read_bytes += size
              else:
                  break
          return min(read_bytes, n)
  
  if __name__ == "__main__":
      global file_content
      buf = ['' for _ in xrange(100)]
      file_content = "a"
      print(buf[:Solution().read(buf, 9)])
      file_content = "abcdefghijklmnop"
      print(buf[:Solution().read(buf, 9)])
  