Python File Operation

 Open() Function

To work with files in Python, we need to use the open() function. There are three options to work with files:

Read (r): This is the default option which opens a file to read.
Write (w): Open a file and write to it. Overwrites any current content in the file.
Append (a): Opens the file and writes to it but instead of overwriting, appends to the file.
Python can work with text or binary (JPG, PNG, MP3, etc.) files.

Open File

I’ll create a text file named “demo.txt” with the following contents:
text_file = open("demo.txt")
print(text_file.read())

In our code, we didn’t specify whether we wanted to read, write, or append to the file. We also didn’t specify whether we wanted to open it in text or binary mode. We don’t have to because the default options are “r” (read) and “t” (text). If you do want to specify our options, it looks like this:

text_file = open("demo.txt", "rt")

print(text_file.read())

So far, so good. We have the contents of our file. However, Python returned it as a string. Wouldn’t it be easier if each line was a separate string? We can do this with the readlines() function:

text_file = open("demo.txt")

print(text_file.readlines())

Close File

In the example above, we opened a file but we never closed it. Closing files is important, especially when you write files.  Some changes in files won’t show up until you close them. In Microsoft Windows, open files are locked which prevents other programs from opening or writing to your files. Here’s an example of how to close your file:

text_file = open("demo.txt")
print(text_file.readlines())
text_file.close()

With Open

Instead of using the separate open() and close() function, we can also use the with block. You put everything you want to do with the file under the with block, and afterward, Python automatically closes the file. Here is an example:

with open("demo.txt") as text_file:
    lines = text_file.readlines()    
print(lines)

Write File

When you write to a file, you overwrite its contents. When the file doesn’t exist, Python creates the file. To write to the file, we need to add the “w” parameter to the open() function. Here is our code:

with open("demo2.txt", "w") as text_file:
    text_file.write("Writing content to this file")
with open("demo2.txt") as text_file:
    lines = text_file.readlines()    
print(lines)

The code above writes a string to the “demo2.txt” file. We could use a text editor to check the contents of the file but since we are using Python, we’ll open it in Python as well.

If you run this code multiple times, it always shows a single line. That’s because the write parameter overwrites the content of our file.

Append File

Instead of overwriting the content of our file, we can append to the file. To do this, you have to use the “a” parameter in the open() function:

with open("demo2.txt", "a") as text_file:
    text_file.write("Writing content to this file")

with open("demo2.txt") as text_file:
    lines = text_file.readlines()

print(lines)

When we run the above code multiple times, you’ll see that Python appends the string to our file. There is one problem though. Python appends the string to the same line.

New Line

If you want to append to a new line, you have to use the \n new line symbol in your string. Here’s our code:

with open("demo2.txt", "a") as text_file:
    text_file.write("\nWriting content to this file")

with open("demo2.txt") as text_file:

    lines = text_file.readlines()   

print(lines)

In the code above, I added the \n new line symbol before my string. Each line we append is now saved in a new line of our file.

Delete File

What if we want to delete a file? We can do this with the OS module and the os.remove() function. This doesn’t work on the embedded Python interpreter so you might want to try this on your own computer. Here is the code:

import os
os.remove("demo2.txt")
or 
import os
file_to_delete = "demo2.txt"
if os.path.exists(file_to_delete):
    os.remove(file_to_delete)
else:
  print("File does not exist.")

DevOps

DevOps is the union of people, process and products to enable continuous delivery of value to end users.

Delivery in iterative and incremental ways to end users.

Collaborate effectively to achieve a common goal. Dev and Ops teams should work on collective organisation goals.

Dev and Ops team should have same goals.

Dev and Ops should follow process that should add continusous value. One way of adding value is by eliminating the waste or waiting time in project.

Get continuous feedback from the customer and use it in the production

Summary:
People coming together for common goals
Adding value to end users (process)
Using tools (products)
Devops => DEv + Ops

The goal of DevOps is to shorten the systems development life cycle while also delivering features, fixes, and updates frequently in close alignment with business objectives. The DevOps approach is to include automation and event monitoring at all steps of the software build. DevOps adoption is estimated to be around 81 percent for larger organizations.

Benefits of using DevOps for companies include:

Better team collaboration and trust
Decreased problem resolution time
Increased quality and stability of code

TCP HALF OPEN

Tcp half open is the state where the client sends SYN to server and server replies with a SYN ACK but the client never send ACK to the server. This will keep TCP session open. The server will keep resending SYN ACK until timeout expires.

This is mainly used for port scanning purposes, just to check ports open on server side. SYN packet will contain the port number of server which it wants to scan. Client will keep retrying with different port numbers until it receives SYN ACK from server. The firewall can be used to block such client to avoid port scan attack.