Python imports are case-sensitive. The fastdownload package exposes a class called FastDownload (PascalCase), not fastdownload. Searching for the lowercase name returns the module itself, not the class, so Python raises ImportError.
The class is FastDownload with a capital F and D. Python imports are case-sensitive — the module name fastdownload and the class name FastDownload are distinct.
from fastdownload import FastDownload
# basic usage
dl = FastDownload()
path = dl.download('https://example.com/file.tar.gz')