这会导致这个错误:
Traceback (most recent call last):
File "/usr/lib/calibre/calibre/utils/ipc/simple_worker.py", line 284, in main
res = {'result':func(*args, **kwargs)}
File "/usr/lib/calibre/calibre/ebooks/oeb/iterator/book.py", line 55, in extract_book
plumber = Plumber(pathtoebook, tdir, log, view_kepub=view_kepub)
File "/usr/lib/calibre/calibre/ebooks/conversion/plumber.py", line 720, in __init__
raise ValueError('Input file must have an extension')
ValueError: Input file must have an extension