nis Module¶

⚠️ REMOVED IN PYTHON 3.13: The nis module was deprecated in Python 3.11 and removed in Python 3.13.

The nis module provides read access to Sun's NIS (Network Information Service, formerly Yellow Pages) — a directory service for distributing user, group, and host maps across a network.

Every call goes to an NIS server, so wall-clock time is dominated by network latency rather than by local computation.

Complexity Reference¶

Operation	Time	Space	Notes
`match(key, mapname, domain=None)`	O(1) + network	O(v)	Server-side hash lookup; v = value size
`cat(mapname, domain=None)`	O(n) + network	O(n)	Whole map as a dict; n = entries
`maps(domain=None)`	O(m) + network	O(m)	List of map names; m = map count
`get_default_domain()`	O(1)	O(1)	Local call, no network

match() is the cheap one: the server indexes the map, so a single lookup does not scan. cat() transfers the entire map.

Looking Up a Single Key¶

import nis

# O(1) server-side lookup plus one network round trip
try:
    entry = nis.match("alice", "passwd.byname")
    print(entry)
except nis.error as exc:
    print(f"lookup failed: {exc}")

Reading a Whole Map¶

import nis

# O(n) - transfers and materializes every entry
users = nis.cat("passwd.byname")
print(len(users))

# Which maps does this domain serve? - O(m)
print(nis.maps())

Choosing Between match() and cat()¶

The tradeoff is round trips versus transfer size:

Access pattern	Prefer	Why
A few known keys	`match()`	O(1) per key, small payloads
Most of the map	`cat()`	One round trip instead of n
Repeated lookups of the same keys	`cat()` once, then a local dict	Amortizes the network cost

import nis

# Bad: n round trips
for name in many_names:
    entry = nis.match(name, "passwd.byname")

# Better: one transfer, then O(1) local lookups
table = nis.cat("passwd.byname")     # O(n), one round trip
for name in many_names:
    entry = table.get(name)          # O(1), no network

Removed in Python 3.13

There is no standard-library replacement. Modern deployments use LDAP (via a third-party client) or the system name-service switch through pwd and grp, which consult NIS transparently where it is configured.

Unix only

nis was never available on Windows, and is absent from builds compiled without NIS support even on Unix.

Version Notes¶

Python 3.11: deprecated (PEP 594)
Python 3.13: removed
Before 3.13: Unix-only, and only when the interpreter was built with NIS support
All versions: match() is a constant-time server lookup; cat() is linear in map size