How to know format of file from a bytes-like object?

ORACLE database that I use stores files in the PDF or ZIP format in the BLOB type. I want to save these files. However, I do not know how to recognize when it is a PDF and when it is ZIP? Is it possible to check which file format BLOB stores inside?

Below is a simple write_file method for saving a file:

def write_file(data, filename):
    with open(filename, 'wb') as f:
        f.write(data)

Here, I fetch the appropriate BLOB with the cursor and I use the write_file method to save the file:

firstRow = cur.fetchone()
write_file(firstRow[0].read(), "blah.zip")

How to recognize when it will be zip and when it will be pdf?

Solution

You can try to check the file signatures by inspecting the bytes you read.

According to this: https://en.wikipedia.org/wiki/List_of_file_signatures

1) A zip file starts with "50 4B 03 04" or "50 4B 05 06" or "50 4B 07 08"

2) A pdf file starts with: "25 50 44 46 2d"

So you can check the first few bytes and check if those are equal to the file signatures - and figure out the file type based on that.