Guide to Python 3

Python 3 guide with just enough basics to begin hacking, note taking from TCM's course

How to read inputs from console

Reading input from STDIN, print output to STDOUT

Sample input

## Input
9
29
7
27

## STDIN
a = int(input())
b = int(input())
c = int(input())
d = int(input())

print(a**b + c**d) ## print to STDOUT

Basic Python 101

Note in the last line than the method "int" ONLY TAKES THE WHOLE NUMBER of a float (etc. returns 29 from 29.9)

Practice Reading Python scripts

Advanced Python 102

Importing, Advanced Strings, Dictionaries

!#/bin/python3
### 1. IMPORTING
import sys # system functions and parameters
from datetime import datetime
print(datetime.now())

from datetime import datetime as dt #import as alias
print(dt.now())

### 2. ADVANCED STRINGS
## SPLIT & JOIN
my_name = 'Davin'
print(my_name[0]) # first letter
print(my_name[:3]) # Dav (excludes the last)
print(my_name[-3:-1]) # vin
test = "hello there I am Davin"
print(test.split(" ")) # split by delimiter space
splitliaolor = test.split()
print(' '.join(splitliaolor))

print("A" in "Apple") # returns true
letter = "A", word = "Apple"
print(letter in word)

String manipulation

string.split(<insert delimiter>)

<delimiter>.join(string)

string.replace(<stringtoreplace> , newstring)

string.find(<string to find>)

Combining List to Dictionary

The Python zip() function accepts iterable items and merges them into a single tuple. The resultant value is a zip object that stores pairs of iterables. You can pass lists, tuples, sets, or dictionaries through the zip() function.

Hosting a web server

For example u might wanna do file transfer to a target machine for download

# go to the folder u want to host (let ur files be available)
### python 2 method
>>> python -m SimpleHTTPServer 80 #port
### python 3 method
>>> python3 -m http.server 80

# file transfer
pip3 install pyftpdlib
python3 -m pyftpdlib -p 21 w

Shitty Port Scanner Script

A good ol homemade nmap scanner to scan for open ports, for this script we are scanning only 50 to 85 as it takes too long!

# program name is scanner.py
#!/usr/bin/env python3
import sys #allow us to use command line arguments etc.
from datetime import datetime as dt
import socket

#Define our targets, make sure theres ip address input
if len(sys.argv) == 2: # this is as python3 scanner.py <ip>, <ip> is argument 1, 2 arguments to python 3      
    target = socket.gethostbyname(sys.argv[1]) #[1] selects ip, translates hostname to IP4   
else:
    print('Invalid amounts of arguments')
    print('Syntax error: Follow python3 scanner.py <ip> la')
    sys.exit()

#Add a pretty banner
print('-' *50)
print('Firing up, Scanning target ' + target )
print('Time started: ' + str(dt.now()))
print('-' * 50)

try:
    for port in range(50,85): # runs port from 50 - 85 cos its shitty
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) #AF_INET is IPV4, SOCK_STREAM is your port   
        socket.setdefaulttimeout(1) #input is a float, detects port not open, then move on after 1s, if not it will hang forever!   
        result = s.connect_ex((target,port)) #if error connection, return error/if no error, returns 0
        print("Checking port {} right now".format(port))
        if result == 0:    # no error
            print("Port {} is open, noice.".format(port))
        s.close()
        
except KeyboardInterrupt: # use ctrl + c to exit program 
    print("\nExiting Program sua")
    sys.exit()
except socket.gaierror:
    print("Hostname cannot be resolved la")
    sys.exit()
    
except socket.error:
    print("Couldnt connect to server walau")
    sys.exit()

results:

Sockets

Explanation for the Echo Server example shown below

TCP sockets are defined as socket.SOCK_STREAM
UDP sockets are defined as socket.SOCK-DGRAM
s.bind() is used to associate the socket with a specific network interface and port number
listen() enables a server to accept() connections. It makes it a “listening” socket
we now have a new socket object from accept(). This is important since it’s the socket that you’ll use to communicate with the client. It’s distinct from the listening socket that the server is using to accept new connections
This reads whatever data the client sends and echoes it back using conn.sendall().

127.0.0.1 : localhost is a hostname that refers to the current device used to access it. It is used to access the network services that are running on the host via the loopback network interface.

Example of a sample implementation : an Echo Server (echo whatever received back to client)

the API calls the server makes to setup a “listening” socket:

socket()
bind()
listen()
accept()

A listening socket does just what it sounds like. It listens for connections from clients. When a client connects, the server calls accept() to accept, or complete, the connection.

#!/usr/bin/env python3

import socket
HOST = '127.0.0.1' # standard loopback interface address 'localhost'
PORT = 65432 #port to listen on

#same as s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
with socket.socket(socket.AF_INET,socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()
    conn, addr = s.accept()
    with conn:
        print('Connected by', addr)
        while True:
            data = conn.recv(1024)
            if not data:
                break
            conn.sendall(data)

Echo Client

#!/usr/bin/env python3

import socket

HOST = '127.0.0.1'  # The server's hostname or IP address
PORT = 65432        # The port used by the server

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((HOST, PORT))
    s.sendall(b'Hello, world')
    data = s.recv(1024)

print('Received', repr(data))

For example,

Without KeyboardInterrupt, ctrl + c will cancel only one loop for <try> and move on to next loop and so on. In python, interpreter throws KeyboardInterrupt exception when the user/programmer presses ctrl – c or del key either accidentally or intentionally. KeyboardInterrupt exception inherits the BaseException and similar to the general exceptions in python, it is handled by try except statement in order to stop abrupt exiting of program by interpreter.

if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        print('Interrupted')
        try:
            sys.exit(0)
        except SystemExit:
            os._exit(0)

Modules (HTTP & FTP Server)

PreviousVulnerability Response Playbook NextWeb Scraping

Last updated 3 years ago