The python the Class IPv4Interface  on the ipaddress module when I try to use the .prefixlen attribute it says that do not exist but is i have access by using ._prefixlen 

if i have on the IPv4Interface class the .netmask attribute and the .nethost attribute Why not the .prefixlen attribute?, 

I reported like a bug as i think that attribute should appear on the IPv4Interface Class

Below test I did 

>>> import ipaddress as ip
>>> addr = ip.ip_interface('192.168.1.1/24')
>>> addr.prefixlen
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'IPv4Interface' object has no attribute 'prefixlen'
>>> addr.netmask
IPv4Address('255.255.255.0')

>>> addr._prefixlen
24

This one works: addr.network.prefixlen.  It took me a while to find out; I find the documentation somewhat confusing in this point.

The docs for current bugfix releases (3.9+) have clear links from the Interface class attribute `network` to the Network class which lists the `prefixlen` attribute. I don't think it can be made clearer - there's two ways to find it - either searching for `prefixlen` and working backwards from network to interface, or following the link from Interface.network.

The link to what Andrei is referring to:
https://docs.python.org/3/library/ipaddress.html#ipaddress.IPv4Network.prefixlen

nosy: + kj, andrei.avk
messages: + msg407699

resolution: not a bug
stage: resolved