pip install python-magic
>>> import magic
>>> magic.from_file("testdata/test.pdf")
'PDF document, version 1.2'
# recommend using at least the first 2048 bytes, as less can produce incorrect identification
>>> magic.from_buffer(open("testdata/test.pdf", "rb").read(2048))
'PDF document, version 1.2'
>>> magic.from_file("testdata/test.pdf", mime=True)
'application/pdf'