how can I convert pdf to image using pdf2image in python on Mac OS X?

I want to convert pdf to image using pdf2image in python on Mac OS X.

from pdf2image.exceptions import (
    PDFInfoNotInstalledError,
    PDFPageCountError,
    PDFSyntaxError
)
# define pdf path
pdf_path = "./pdf_file/ooo.pdf"

# convert pdf to image（1200dpi）
images = convert_from_path(str(pdf_path), 1200)
# save image files one by one
image_dir = "./image_file"
for i, image in enumerate(images):
    file_name = pdfpath + "{:02d}".format(i + 1) + ".jpeg"
    image_path = image_dir / file_name
    # save JPEG
    image.save(str(image_path), "JPEG")

then I get the error message like

TypeError                                 Traceback (most recent call last)
<ipython-input-19-26e2710189ca> in <module>
     13 for i, image in enumerate(images):
     14     file_name = pdfpath + "{:02d}".format(i + 1) + ".jpeg"
---> 15     image_path = image_dir / file_name
     16     # save JPEG
     17     image.save(str(image_path), "JPEG")

TypeError: unsupported operand type(s) for /: 'str' and 'str'

I cannot understand what is happening. Please help!