socket.makefile raises ValueError when mode = 'rt'

[Antoon Pardon]

This is using python 3.2.

I am writing somekind of wrapper around the ftplib. So
that you can work with it as if you are working with
local files.

The idea is that you start with making a connection like

rmt = FTP(...)

and then do something like the following

rmtfl = rmt.open("rmtfilename", "rt")
for ln in rmtfl:
    treat(ln)

This is part of the code:

class ftpfile:
    def __init__(self, cn, rfn, mode, bound = False):
        self.ftp = cn
        self.bound = bound
        if 'b' in mode:
            self.ftp.voidcmd('TYPE I')
        else:
            self.ftp.voidcmd('TYPE A')
        if 'r' in mode:
            self.cnct =  self.ftp.transfercmd("RETR %s" % rfn)
            self.fl = self.cnct.makefile(mode)
        elif 'w' in mode:
            self.cnct =  self.ftp.transfercmd("STOR %s" % rfn)
            self.fl = self.cnct.makefile(mode, newline = '\r\n')
        else:
            raise ValueError("%s: invalide mode" % mode)

The problem is with makefile. If mode contains a "t" I get
the following traceback:

Traceback (most recent call last):
  File "ftputil.tpy", line 14, in test_textftp
    rmtfl1 = rmt.open('ftp1.py', 'wt')
  File "/local/home/apardon/src/projecten/py3lib/ftputil.py", line 76,
in open
    return ftpfile(ftp, fn, mode, True)
  File "/local/home/apardon/src/projecten/py3lib/ftputil.py", line 15,
in __init__
    self.fl = self.cnct.makefile(mode, newline = '\r\n')
  File "/usr/lib/python3.2/socket.py", line 151, in makefile
    raise ValueError("invalid mode %r (only r, w, b allowed)")
ValueError: invalid mode %r (only r, w, b allowed)

But the documentation states:
socket.makefile(mode='r', buffering=None, *, encoding=None, errors=None,
newline=None)
    Return a file object associated with the socket. The exact returned
type depends on the arguments given to makefile(). These arguments are
interpreted the same way as by the built-in open() function.

And since 't' is allowed in the mode of the built-in open() function I
would consider this a bug.
Unless I am missing something?