flashing pico with stm32loader.py

I am trying to flash an STM32F0 device and added the ID to the list by modifying the python source as follows:

# Takes chip IDs (obtained via Get ID command) to human-readable names
CHIP_ID_STRS = {0x410: 'STM32F1, performance, medium-density',
                0x411: 'STM32F2',
                0x412: 'STM32F1, performance, low-density',
                0x413: 'STM32F4',
                0x414: 'STM32F1, performance, high-density',
                0x416: 'STM32L1, performance, medium-density',
                0x418: 'STM32F1, connectivity',
                0x420: 'STM32F1, value, medium-density',
                0x428: 'STM32F1, value, high-density',
		0x430: 'STM32F1, performance, XL-density',
		0x448: 'STM32F0, performance, hi-density'
		}

Then I invoke the python script as follows:

Proton:STM32 wayne$ python ./stm32loader.py -b 115200 -V -p /dev/tty.usbserial-FTGVKLRW -evw ./BL.bin

then I get the response:

Open port /dev/tty.usbserial-FTGVKLRW, baud 115200
Reading data from ./BL.bin
Traceback (most recent call last):
  File "./stm32loader.py", line 548, in <module>
    data = read(args[0])
  File "./stm32loader.py", line 442, in read
    if bytes.startswith('\x7FELF'):
TypeError: startswith first arg must be bytes or a tuple of bytes, not str

Any thoughts on whether this is python script problem? or something with the device I am trying to program? I have held the boot pin button while resetting the device.

I should note that I am on macOS Sierra (10.12.1)