Table of Contents

1. Background
2. Log variables / output messages
3. Run a command with realtime stdout
4. Run a command with blocked stdout
5. Print with Color
6. Get a single character from user input
7. Handle network interface addresses

Background

Q: What exactly is this module called z2?

A: Various code bites to keep my python code DRY.

Log variables / output messages

## LogIt() is implemented by loguru.
##  loguru is a complete python logging rewrite.
##
##  See https://github.com/Delgan/loguru

from z2.utils import LogIt

LogIt().info("You forgot to eat your corn flakes")

Run a command with streaming realtime stdout

There are a couple of zrun recipies to consider...

1. Run three pings and see output in realtime.

• realtime=True allows you to watch individual pings as they happen...
• add all stdout to a list

from z2.process import zrun

## Call z2.process.zrun()...
## - Watch individual pings as they happen... like you ran it in bash / zsh / ??
## - add all output to a list
output = list(zrun("ping -c3 172.16.1.1", print_stdout=True, realtime=True))

print(output)

2. Run non-stop pings and act on individual pings.

• realtime=True allows you to watch individual pings as they happen...
• add all stdout to a list

from datetime import datetime
import errno

from z2.process import zrun

def act_on_ping(condition=None, now=datetime.now()):
    assert isinstance(condition, str)

    if condition=="foo":
        # Do something...
        pass

    # Much more here...


## Call z2.process.zrun()...
## - Watch individual pings as they happen... like you ran it in bash / zsh / ??
## - add all output to a list

for ii in zrun("ping -c5 -O 172.16.1.1", print_stdout=True, realtime=True):

    if isinstance(ii, str):
        output.append(ii)

    if isinstance(ii, str) and "no answer" in ii.lower():
        # Lost a ping -> "no answer yet for icmp_seq=1"
        #     do something here
        act_on_ping(condition="ping_timeout")

    elif isinstance(ii, int) and ii==errno.EWOULDBLOCK:
        # This is normal while waiting on ping stdout...
        print("    errno.EWOULDBLOCK")
        pass

print(output)

Run a command with blocked stdout

1. Run three pings with blocked stdout

• realtime=False blocks stdout
• results are returned in a list()

from z2.process import zrun

## Call z2.process.zrun()...
## - stdout is blocked during cmd execution
## - return all output as a list of strings
output = list(zrun("ping -c3 172.16.1.1", print_stdout=True, realtime=False))

print(output)

getchar() - Get a single character from user input

getchar() is a function to read a single letter from stdin and return it.

from z2.strings import getchar

input_character = getchar(prompt_text="What letter are you thinking of? ")
print(f"The character input was '{input_character}'")

input_character = getchar(
    prompt_text="What letter are you thinking of? ",
    allowed_chars=set({"a", "b", "c"}),
    )
print(f"The input restricted character was '{input_character}'")

Print with Color

from z2.strings import C

# Print with green, orange
print(C.GREEN + "Hello" + C.YELLOW + " World" + C.ENDC)

Handle network interface addresses

Most network interfaces take an IPv4 or IPv6 address format with a network mask or a mask-length. However, when you try to store both address and mask in Python stdlib, you hit a problem. IPv4Address() does not process a mask, and IPv4Network() does not store "host-bits". Consider the following:

>>> # IPv4Address() and IPv4Network() are from python stdlib.
>>> from ipaddress import IPv4Address, IPv4Network
>>> intfAddr = IPv4Address("1.1.1.200/24")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/python37/lib/python3.7/ipaddress.py", line 1300, in __init__
    raise AddressValueError("Unexpected '/' in %r" % address)
ipaddress.AddressValueError: Unexpected '/' in '1.1.1.200/24'
>>>
>>>
>>> ### IPv4Network() does not store "host bits", only "network bits".
>>> ### As such, IPv4Network() is **useless** to hold network devices'
>>> ### real-life needs (to store the interface address and mask).
>>>
>>> intfAddr = IPv4Network("1.1.1.200/24")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/python37/lib/python3.7/ipaddress.py", line 1536, in __init__
    raise ValueError('%s has host bits set' % self)
ValueError: 1.1.1.200/24 has host bits set
>>> intfAddr = IPv4Network("1.1.1.200/24", strict=False)
>>> intfAddr
IPv4Network('1.1.1.0/24')
>>> ### Above ^^^^^^ we see that IPv4Network() strips .200 from the
>>> ### address.

Keeping the interface address and mask is supported out of the box with
z2.IPv4Obj(). See below...

>>> from z2 import IPv4Obj
>>> intfAddr = IPv4Obj("1.1.1.200/24")
>>>
>>> intfAddr
<IPv4Obj 1.1.1.200/24>
>>>