Doubt with IF and LISTS python3

Question

I’m new to the python language, but I started to develop a script to manage linux servers etc... I have a little problem in a code snippet:

def rotear():

    print(" \n Disponível: \n"), os.system("ifconfig|grep eth|cut -c 1-4")
    interface_internet = input(" \n Digite a Interface de Internet: ")
    if interface_internet != ethers[0]:
            print("Nao deu certo!")

Next, I listed the network interfaces, I put together this snippet of code, but I wanted to figure out a way to get the list of network interfaces, and make a condition true or false to proceed with the code

ex:

listed the interface with the ifconfig command | grep Eth | cut -c 1-4

eth0

eth1

if interface_internet is different from one of the above listings, do this otherwise, do that

I wanted a solution on this...

So I put the code:

def rotear():
    ethers = ['eth0','eth1','eth2','wlan0','wlan1','ath0','ath1']
    print(" \n Listando Interfaces de Rede(s)..."),time.sleep(1)
    print(" \n Disponível: \n"), os.system("ifconfig|grep eth|cut -c 1-4")
    interface_internet = input(" \n Digite a Interface de Internet: ")
    for device in ethers:
        if interface_internet == device:
            header(" \n 1 - Habilitar Roteamento")
            header(" 2 - Desabilitar Roteamento\n")
            encaminhar = input(" Escolha uma Opção de Roteamento:")
            if encaminhar == "1":
                os.system("echo 1 > /proc/sys/net/ipv4/ip_forward")
                os.system("iptables -t nat -A POSTROUTING -o %s -j MASQUERADE" % (interface_internet))
                sucess(" \n Roteamento Habilitado Com Sucesso..."),tcl()
            elif encaminhar == "2":
                os.system("echo 0 > /proc/sys/net/ipv4/ip_forward")
                sucess(" \n Roteamento Desabilitado Com Sucesso..."),tcl()
        else:
            fail(" \n Atenção: Valor Inválido. ")

only I’m in trouble, if I put the value: eth2 for example, he makes two loops, saying that the value ta invalido until right... how do I fix it now?

Answer 1

To list all network interfaces, you can use the python-nmap. Take a look to find the correct command for this.
After grabbing all interfaces, put them in a list and then use a for to test conditions in each of the interfaces, something like this:

for device in ethers:
    if interface_internet == device:
        fazer X
    else:
        fazer Y

ethers will be your list with all network interfaces.
The for will loop to each interface in the list, calling it device. So he checks if the device is equal to interface_internet, and then makes the decisions.

Answer 2

It enters 2 times in the loop and error until finding because it is testing value by list value to see if it is equal to 'eth2'. First forehead with eth0 afterward eth1 and only then with eth2.

To check if the value is inside the list ethers you must use the reserved word in as I did in the code below, if variavel in lista:....

def rotear():
    ethers = ['eth0','eth1','eth2','wlan0','wlan1','ath0','ath1']
    print(" \n Listando Interfaces de Rede(s)..."),time.sleep(1)
    print(" \n Disponível: \n"), os.system("ifconfig|grep eth|cut -c 1-4")
    interface_internet = input(" \n Digite a Interface de Internet: ")
    if interface_internet in ethers:
        header(" \n 1 - Habilitar Roteamento")
        header(" 2 - Desabilitar Roteamento\n")
        encaminhar = input(" Escolha uma Opção de Roteamento:")
        if encaminhar == "1":
            os.system("echo 1 > /proc/sys/net/ipv4/ip_forward")
            os.system("iptables -t nat -A POSTROUTING -o %s -j MASQUERADE" % (interface_internet))
            sucess(" \n Roteamento Habilitado Com Sucesso..."),tcl()
        elif encaminhar == "2":
            os.system("echo 0 > /proc/sys/net/ipv4/ip_forward")
            sucess(" \n Roteamento Desabilitado Com Sucesso..."),tcl()
    else:
        fail(" \n Atenção: Valor Inválido. ")

Answer 3

If Voce is going to use python for infrastructure management tasks in the linux environment, my suggestion is that you do, first of all; this:

pip install plumbum

Plubum:

(tl;dr)
With this package you can run most shell commands, to answer your question, I ran a ifconfig | grep simple, just to grab the lines in which the string appears Eth, but you can compose the command you want. The result of the command is placed in a list and then... Well... I’m not gonna get too blah blah, because I explained in the code itself.

# Para execução de comandos shell
from plumbum.cmd import grep, ifconfig
from plumbum import FG, BG
# Firula
import pprint  

# Monta o comando ifconfig (ifconfig | grep Eth)
ifc = ifconfig | grep["Eth"]

# Executa o comando
f = ifc & BG
output = f.stdout

# Atribui a saida do comando a um objeto tipo lista do pyton
lst = output.splitlines()

pprint.pprint(lst)

Result of pprint:

['docker0   Link encap:Ethernet  Endereço de HW 02:42:bb:5c:52:96  ',
 'enp3s0    Link encap:Ethernet  Endereço de HW 10:c3:7b:c4:21:e4  ']

Functions for list searches:

# Pesquisa restritiva, o conteudo da variável tem que "casar" com uma linha inteira na lista
def search1(var):
    return var if var in lst else 'Não encontrado'

# Pesquisa não restritiva, basta uma substring dentro de um dos elementos da lista
def search2(var):
    result = [s for s in lst if var in s]
    return var if len(result)>0 else 'Não encontrado'

Searches on the list:

# Variável a ser pesquisada na lista
str1 = 'docker0'
str2 = 'docker0   Link encap:Ethernet  Endereço de HW 02:42:bb:5c:52:96  '

print ("REALIZANDO BUSCAS\n")
print ('Busca restritiva')
print ("str1 : ", search1(str1))
print ("str2 : ", search1(str2))
print ('\nBusca não restritiva')
print ("str1 : ", search2(str1))
print ("str2 : ", search2(str2))

Search results:

Busca restritiva
str1 :  Não encontrado
str2 :  docker0   Link encap:Ethernet  Endereço de HW 02:42:bb:5c:52:96  

Busca não restritiva
str1 :  ['docker0   Link encap:Ethernet  Endereço de HW 02:42:bb:5c:52:96  ']
str2 :  ['docker0   Link encap:Ethernet  Endereço de HW 02:42:bb:5c:52:96  ']

Using the command if:

if str1 in search1(str1):
    print ('str1 foi encontrada na busca restritiva')
else:
    print ('str1 não foi encontrada na busca restritiva')

if str2 in search1(str2):
    print ('str2 foi encontrada na busca restritiva')
else:
    print ('str2 não foi encontrada na busca restritiva')

if str1 in search2(str1):
    print ('str1 foi encontrada na busca não restritiva')
else:
    print ('str1 não foi encontrada na busca não restritiva')

if str2 in search2(str2):
    print ('str2 foi encontrada na busca não restritiva')
else:
    print ('str2 não foi encontrada na busca não restritiva')    

Output for the commands if's:

str1 não foi encontrada na busca restritiva
str2 foi encontrada na busca restritiva
str1 não foi encontrada na busca não restritiva
str2 foi encontrada na busca não restritiva  

Final consideration:
Of course the function search1(var) can be considered unnecessary if we were to consider only the restrictive search, because it would be enough to do:

if var not in lst:
   print ('Não encontrada')

But depending on the context, one can join the two functions (restrictive and non-restrictive search) in one, for flexibility and practicality gain.

See the code running on that notebook jupyter.