Inheritance basics#
Inheritance allows creation of new classes based on existing ones. There are child and parents classes: child class inherits parent class. In inheritance, child class inherits all methods and attributes of parent class.
Example of ConnectSSH class that performs SSH connection using paramiko:
import paramiko
import time
class ConnectSSH:
def __init__(self, ip, username, password):
self.ip = ip
self.username = username
self.password = password
self._MAX_READ = 10000
client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
client.connect(
hostname=ip,
username=username,
password=password,
look_for_keys=False,
allow_agent=False)
self._ssh = client.invoke_shell()
time.sleep(1)
self._ssh.recv(self._MAX_READ)
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self._ssh.close()
def close(self):
self._ssh.close()
def send_show_command(self, command):
self._ssh.send(command + '\n')
time.sleep(2)
result = self._ssh.recv(self._MAX_READ).decode('ascii')
return result
def send_config_commands(self, commands):
if isinstance(commands, str):
commands = [commands]
for command in commands:
self._ssh.send(command + '\n')
time.sleep(0.5)
result = self._ssh.recv(self._MAX_READ).decode('ascii')
return result
This class will be used as the basis for classes that are responsible for connecting to devices of different vendors. For example, CiscoSSH class will be responsible for connecting to Cisco devices and will inherit ConnectSSH class.
Inheritance syntax:
class CiscoSSH(ConnectSSH):
pass
After that, all ConnectSSH methods and attributes are available in CiscoSSH class:
In [3]: r1 = CiscoSSH('192.168.100.1', 'cisco', 'cisco')
In [4]: r1.ip
Out[4]: '192.168.100.1'
In [5]: r1._MAX_READ
Out[5]: 10000
In [6]: r1.send_show_command('sh ip int br')
Out[6]: 'sh ip int br\r\nInterface IP-Address OK? Method Status Protocol\r\nEthernet0/0 192.168.100.1 YES NVRAM up up \r\nEthernet0/1 192.168.200.1 YES NVRAM up up \r\nEthernet0/2 19.1.1.1 YES NVRAM up up \r\nEthernet0/3 192.168.230.1 YES NVRAM up up \r\nLoopback0 4.4.4.4 YES NVRAM up up \r\nLoopback33 3.3.3.3 YES manual up up \r\nLoopback90 90.1.1.1 YES manual up up \r\nR1#'
In [7]: r1.send_show_command('enable')
Out[7]: 'enable\r\nPassword: '
In [8]: r1.send_show_command('cisco')
Out[8]: '\r\nR1#'
In [9]: r1.send_config_commands(['conf t', 'int loopback 33',
...: 'ip address 3.3.3.3 255.255.255.255', 'end'])
Out[9]: 'conf t\r\nEnter configuration commands, one per line. End with CNTL/Z.\r\nR1(config)#int loopback 33\r\nR1(config-if)#ip address 3.3.3.3 255.255.255.255\r\nR1(config-if)#end\r\nR1#'
After inheriting all methods of parent class, child class can:
leave them unchanged
rewrite them completely
supplement method
add your methods
In CiscoSSH class you have to create __init__ method and
add parameters to it:
enable_password- enable passworddisable_paging- is responsible for paging turning on/off
Method __init__ can be created entirely from scratch but basic SSH
connection logic is the same in ConnectSSH and CiscoSSH, so it is better
to add necessary parameters and call __init__ method of ConnectSSH
class for connection. There are several options for calling parent method,
for example, all of these options will call send_show_command method
of parent class from child class CiscoSSH:
command_result = ConnectSSH.send_show_command(self, command)
command_result = super(CiscoSSH, self).send_show_command(command)
command_result = super().send_show_command(command)
The first version of ConnectSSH.send_show_command explicitly specifies the
name of parent class - this is the most understandable version for perception,
but its disadvantage is that when a parent class name is changed the name will
have to be changed in all places where parent class methods were called.
This option also has disadvantages when using multiple inheritance.
The second and third options are essentially equivalent but the third option
is shorter, so we will use it.
CiscoSSH class with __init__ method:
class CiscoSSH(ConnectSSH):
def __init__(self, ip, username, password, enable_password,
disable_paging=True):
super().__init__(ip, username, password)
self._ssh.send('enable\n')
self._ssh.send(enable_password + '\n')
if disable_paging:
self._ssh.send('terminal length 0\n')
time.sleep(1)
self._ssh.recv(self._MAX_READ)
Method __init__ in CiscoSSH class added enable_password and
disable_paging parameters and uses them accordingly to enter enable
mode and disable paging.
Example:
In [10]: r1 = CiscoSSH('192.168.100.1', 'cisco', 'cisco', 'cisco')
In [11]: r1.send_show_command('sh clock')
Out[11]: 'sh clock\r\n*11:30:50.280 UTC Mon Aug 5 2019\r\nR1#'
Now when connecting, switch enters enable mode and paging is disabled by default, so you can try to run a long command like sh run.
Another method that should be further developed is send_config_commands
method: since CiscoSSH class is designed to work with Cisco, you can add
switching to configuration mode before commands and exit after.
class CiscoSSH(ConnectSSH):
def __init__(self, ip, username, password, enable_password,
disable_paging=True):
super().__init__(ip, username, password)
self._ssh.send('enable\n')
self._ssh.send(enable_password + '\n')
if disable_paging:
self._ssh.send('terminal length 0\n')
time.sleep(1)
self._ssh.recv(self._MAX_READ)
def config_mode(self):
self._ssh.send('conf t\n')
time.sleep(0.5)
result = self._ssh.recv(self._MAX_READ).decode('ascii')
return result
def exit_config_mode(self):
self._ssh.send('end\n')
time.sleep(0.5)
result = self._ssh.recv(self._MAX_READ).decode('ascii')
return result
def send_config_commands(self, commands):
result = self.config_mode()
result += super().send_config_commands(commands)
result += self.exit_config_mode()
return result
Example of send_config_commands method use:
In [12]: r1 = CiscoSSH('192.168.100.1', 'cisco', 'cisco', 'cisco')
In [13]: r1.send_config_commands(['interface loopback 33',
...: 'ip address 3.3.3.3 255.255.255.255'])
Out[13]: 'conf t\r\nEnter configuration commands, one per line. End with CNTL/Z.\r\nR1(config)#interface loopback 33\r\nR1(config-if)#ip address 3.3.3.3 255.255.255.255\r\nR1(config-if)#end\r\nR1#'