sys.stdout.write和print和sys.stdout.flush

 1 """
 2 sys.stdout.write(string)
 3 　　Write string to stream.
 4 　　Returns the number of characters written (which is always equal to the length of the string).
 5 
 6 print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
 7 　　Prints the values to a stream, or to sys.stdout by default.
 8 
 9 　　Optional keyword arguments:
10 　　file:  a file-like object (stream); defaults to the current sys.stdout.
11 　　sep:   string inserted between values, default a space.
12 　　end:   string appended after the last value, default a newline.
13 　　flush: whether to forcibly flush the stream.
14 """

1 import sys
2 f = open('test.txt', 'w')
3 print('print write into file', file=f)
4 f.close()

1 flush() 
2     method of _io.TextIOWrapper instance
3     Flush write buffers, if applicable.
4     
5     This is not implemented for read-only and non-blocking streams.

1 import time
2 import sys
3  
4 for i in range(5):
5     print(i)
6     sys.stdout.flush()
7     time.sleep(1)