PYserial basics?

[bako]

import serial
import time
ser = serial.Serial("/dev/ttyS0", baudrate=115200)
W_buf = ["AT\r\n", "AT+CMGS=\"15555555555\"\r\n", "Helloworld"]
ser.write(W_buf[0])
ser.flushInput()

Error:
Traceback (most recent call last):
  File "send_message.py", line 3, in <module>
    ser = serial.Serial("/dev/ttyS0", baudrate=115200)
AttributeError: 'module' object has no attribute 'Serial'

#pythonnoob

I just copied and pasted the code and I don't really get this error message. The pyserial package was installed using PIP. What am I doing wrong?