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.IX Title "libnbd-python 3"
.TH libnbd-python 3 2025-12-16 libnbd-1.24.0 LIBNBD
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.SH NAME
libnbd\-python \- how to use libnbd from Python
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 5
\& #!/usr/bin/python3
\& import nbd
\& h = nbd.NBD()
\& h.connect_uri("nbd://localhost")
\& sector = h.pread(512, 0)
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This manual page documents how to use libnbd to access Network Block
Device (NBD) servers from the Python programming language.  The Python
bindings work very similarly to the C bindings so you should start by
reading \fBlibnbd\fR\|(3).
.PP
There is a convenient interactive command line shell called
\&\fBnbdsh\fR\|(1) which makes it easier to play with the Python API.
.PP
Detailed documentation of the Python API is provided in the Python
code.  To read it, open \fBnbdsh\fR\|(1) and type:
.PP
.Vb 1
\& help(nbd)
.Ve
.PP
There are some example Python scripts in the libnbd source repository
under \fIpython/examples\fR or see
https://gitlab.com/nbdkit/libnbd/tree/master/python/examples.
.SH HANDLES
.IX Header "HANDLES"
Create a libnbd handle by calling \f(CW\*(C`nbd.NBD()\*(C'\fR.
.PP
You can either close the handle explicitly with \f(CW\*(C`h.close()\*(C'\fR (added in
libnbd\ 1.16), or it will be closed automatically when it goes out
of scope.
.PP
Calling any method on a handle that has been closed will raise
\&\f(CW\*(C`nbd.ClosedHandle\*(C'\fR.
.SH ERRORS
.IX Header "ERRORS"
Errors from API calls are turned into the Python \f(CW\*(C`nbd.Error\*(C'\fR
exception (derived from \f(CW\*(C`Exception\*(C'\fR).  The \f(CW\*(C`nbd.Error\*(C'\fR object has
three properties of interest:
.ie n .IP """ex.string""" 4
.el .IP \f(CWex.string\fR 4
.IX Item "ex.string"
The full error message as a printable string.
.Sp
Example: \f(CW"nbd_pread: invalid state: START: the handle must be
connected with the server: Transport endpoint is not connected"\fR
.ie n .IP """ex.errnum""" 4
.el .IP \f(CWex.errnum\fR 4
.IX Item "ex.errnum"
The errno object (from the Python \f(CW\*(C`errno\*(C'\fR module), \fIif\fR this is
available.  Not all errors that are raised will have an errno.
.Sp
Example: \f(CW\*(C`errno.EINVAL\*(C'\fR
.Sp
For common error codes see "Errno" in \fBlibnbd\fR\|(3).
.ie n .IP """ex.errno""" 4
.el .IP \f(CWex.errno\fR 4
.IX Item "ex.errno"
The errno as a string (or \f(CW\*(C`None\*(C'\fR if this is not available).
.Sp
Example: \f(CW"ENOTCONN"\fR
.SH BUFFERS
.IX Header "BUFFERS"
Synchronous calls (eg. \f(CW\*(C`h.pwrite\*(C'\fR, \f(CW\*(C`h.pread\*(C'\fR) take and return normal
Python \f(CW\*(C`bytearray\*(C'\fRs.
.PP
Asynchronous calls (eg. \f(CW\*(C`h.aio_pwrite\*(C'\fR, \f(CW\*(C`h.aio_pread\*(C'\fR) use the
\&\f(CW\*(C`nbd.Buffer\*(C'\fR type, which is a persistent, modifiable, zero\-copy
buffer.  The buffer also supports indexing and slicing.  These are
more complicated to use, and in particular the caller must ensure the
buffer remains valid while the asynchronous operation is taking place.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBlibnbd\fR\|(3),
\&\fBnbdsh\fR\|(1).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
.PP
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.
.PP
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110\-1301 USA