来自builtins.py：
def print(self, *args, sep=' ', end='\n', file=None): # known special case of print
"""
print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
Prints the values to a stream, or to sys.stdout by default.
Optional keyword arguments:
file: a file-like object (stream); defaults to the current sys.stdout.
sep: string inserted between values, default a space.
end: string appended after the last value, default a newline.
flush: whether to forcibly flush the stream.
"""
pass
联系，看着理解。
print('abc','def','ghi\n',sep='***',end='**')
print('abc','def','ghi',sep='***',end='**')
print('abc\n','def\n','ghi',sep='***',end='**')
输出如下：
abc***def***ghi
**abc***def***ghi**abc
***def
***ghi**
