RSAKey.from_private_key doesn't work with io.BytesIO object in python3

[mirrt]

when using io.BytesIO to create file like object and pass than object to RSAKey.from_private_key in python3 like this

ssh_key = '-----BEGIN DSA PRIVATE KEY-----\n'\
'<keydata>'\
'-----END DSA PRIVATE KEY-----\n'

file_obj = io.BytestIO(ssh_key)
pkey = RSAKey.from_private_key(file_obj)

it raises an error

the issue is here

    def _read_private_key(self, tag, f, password=None):
        lines = f.readlines()
        start = 0
        beginning_of_key = "-----BEGIN " + tag + " PRIVATE KEY-----"
        while start < len(lines) and lines[start].strip() != beginning_of_key:
            start += 1
        if start >= len(lines):
            raise SSHException("not a valid " + tag + " private key file")

readline returns a list of binary and this comparison fails

lines[start].strip() != beginning_of_key

[ploxiln]

you could use io.StringIO(ssh_key) instead