Update docs

Author: 777GE90

Doc/library/ipaddress.rst

@@ -739,7 +739,7 @@ dictionaries.
          Traceback (most recent call last):
             File "<stdin>", line 1, in <module>
                raise ValueError(
-         ValueError: next prefix must be between 1 and 32
+         ValueError: prefix must be between 1 and 32
          >>> IPv4Network('255.255.255.0/24').next_network()
          Traceback (most recent call last):
             File "<stdin>", line 1, in <module>
@@ -748,6 +748,36 @@ dictionaries.
 
       .. versionadded:: 3.16
 
+   .. method:: prev_network(prev_prefix=None)
+
+      Finds the previous closest network of prefix size *prev_prefix*.  If
+      *prev_prefix=None*, then the current network prefix will be used.
+      Returns a single network object.
+
+      Raises :exc:`ValueError` if *prev_prefix* is out of range or no further
+      network of the requested size exists.
+
+         >>> IPv4Network('192.0.2.0/24').prev_network()
+         IPv4Network('192.0.1.0/24')
+         >>> IPv4Network('192.0.2.0/24').prev_network(prev_prefix=25)
+         IPv4Network('192.0.1.128/25')
+         >>> IPv4Network('192.0.2.0/24').prev_network(prev_prefix=23)
+         IPv4Network('192.0.0.0/23')
+         >>> IPv4Network('192.0.80.0/22').prev_network(prev_prefix=18)
+         IPv4Network('192.0.0.0/18')
+         >>> IPv4Network('192.0.80.0/22').prev_network(prev_prefix=50)
+         Traceback (most recent call last):
+            File "<stdin>", line 1, in <module>
+               raise ValueError(
+         ValueError: prefix must be between 1 and 32
+         >>> IPv4Network('0.0.0.0/24').prev_network()
+         Traceback (most recent call last):
+            File "<stdin>", line 1, in <module>
+               raise ValueError(
+         ValueError: out of address space, cannot make another /24 network
+
+      .. versionadded:: 3.16
+
 .. class:: IPv6Network(address, strict=True)
 
    Construct an IPv6 network definition.  *address* can be one of the following:
@@ -820,6 +850,7 @@ dictionaries.
    .. method:: subnet_of(other)
    .. method:: supernet_of(other)
    .. method:: next_network(next_prefix=None)
+   .. method:: prev_network(prev_prefix=None)
    .. method:: compare_networks(other)
 
       Refer to the corresponding attribute documentation in

Doc/whatsnew/3.16.rst

@@ -321,6 +321,9 @@ ipaddress
 Add :meth:`~ipaddress.IPv4Network.next_network` and
 :meth:`~ipaddress.IPv6Network.next_network` methods to find the next nearest
 network with a specific prefix size.
+Add :meth:`~ipaddress.IPv4Network.prev_network` and
+:meth:`~ipaddress.IPv6Network.prev_network` methods to find the previous nearest
+network with a specific prefix size.
 
 
 logging

Misc/NEWS.d/next/Library/2021-01-09-18-40-15.bpo-42861.T7Ge9O.rst

@@ -1,2 +1,4 @@
-Add :meth:`~ipaddress.IPv4Network.next_network` and
-:meth:`~ipaddress.IPv6Network.next_network`.  Patch by Faisal Mahmood.
+Add :meth:`~ipaddress.IPv4Network.next_network`,
+:meth:`~ipaddress.IPv6Network.next_network`,
+:meth:`~ipaddress.IPv4Network.prev_network` and
+:meth:`~ipaddress.IPv6Network.prev_network`. Patch by Faisal Mahmood.