nis Module Complexity¶

The nis module reads maps from Sun's NIS (Network Information Service, formerly Yellow Pages), a directory service that distributes user, group and host tables across a network. Every call but get_default_domain() makes requests to an NIS server; what a call controls is how many requests it makes and how much it brings back.

Removed in Python 3.13

Deprecated in Python 3.11 and removed in Python 3.13 by PEP 594. The page covers the module as it is on Python 3.11 and 3.12 on Unix, in an interpreter built with NIS support; the examples also need a machine bound to an NIS domain that serves a non-empty passwd.byname.

n is the entries in one map and m is the maps a domain serves. The bounds treat a key or value as short - a line of a system table - so decoding one is O(1). match(), cat() and maps() take the domain as a string and default to get_default_domain() when it is left out; None is not accepted. Pass the map name by position, as its keyword is map rather than mapname. A map name may be a nickname - passwd, group, hosts, networks, protocols, services, ethers or aliases - which is turned into the full name, such as passwd.byname, without a request.

Complexity Reference¶

Functions¶

Operation	Time	Space	Notes
`nis.match(key, mapname, domain=default_domain)`	O(1) plus one request	O(1)	Returns the value as a `str`, or raises `nis.error` when the key or map is missing
`nis.cat(mapname, domain=default_domain)`	O(n) plus one request	O(n)	Returns the whole map as a new `dict` of `str` to `str`, streamed over one connection
`nis.maps(domain=default_domain)`	O(m) plus several requests	O(m)	Returns a `list` of map names. Asks for the master server of each nickname's map until one answers, then connects to that master
`nis.get_default_domain()`	O(1)	O(1)	Reads the host's domain name; no request

Exceptions¶

Operation	Time	Space	Notes
`nis.error`	O(1)	O(1)	Raised when a call fails, such as for a missing key or map

Looking Up Keys¶

match() costs one request whatever the map's size. cat() transfers every entry in one request, so it is the wrong call for one key, and the right one for most of the map: n calls to match() are n round trips, where one cat() and a local dict lookup per key are one.

import nis

users = nis.cat('passwd')  # O(n) - every entry, over one connection
name, line = next(iter(users.items()))
assert nis.match(name, 'passwd') == line  # O(1) plus one request

try:
    nis.match('no such user', 'passwd.byname')
except nis.error as error:
    assert str(error)  # the NIS library's message
else:
    raise AssertionError('a missing key returned a value')

Listing a Domain's Maps¶

get_default_domain() asks the local host, not a server. maps() makes several requests: it looks for the master server of the standard maps one nickname at a time, then connects to that master for the list.

import nis

domain = nis.get_default_domain()  # O(1) - no request
maps = nis.maps(domain)  # O(m) plus several requests
assert 'passwd.byname' in maps

Performance Best Practices¶

✅ Do:

Use match() for a few keys; each is one request whatever the map's size
Call cat() once and look keys up in the dict when you need most of a map, or the same keys repeatedly
Use pwd and grp for users and groups; through the C library's name service they consult NIS where the host is configured for it, and they outlive this module

❌ Avoid:

Calling match() in a loop over a whole map - one round trip per key
Calling cat() to read one key - it transfers every entry
Passing domain=None - it raises TypeError; leave the argument out instead

Version Notes¶

Python 3.11+: import nis emits a DeprecationWarning
Python 3.13+: The module is removed; import nis raises ModuleNotFoundError

pwd - the user database, which reads NIS through the C library where it is configured
grp - the group database, likewise