In this chapter we will work with opening and closing files.

Out of the box, Python comes with standard functionality built in to work with basic text files:

• .txt
• .csv
• any file that's not encoded (text file saved as a .log or .ini file)

Working with files can be as easy or as complex as you need/want it to be.

Why do I say this? Because Python comes with file handling built-in as well as it has several exeternal modules and packages that do the same as well as work on specialized file types such as SQL, PDF, Images, Audio, HTML, JSON, etc.

The open() statement

To open a text file in python is pretty straight forward with the open() function.

my_file = open("targets.txt", "r")
print(my_file.read())

The open() function, assigns the file to the variable my_file. We then use the read() function to read the files contents and assign it to the our variable. A major issue with this is that you have to include the close() function, as the file will remain perterually opened with can leave to dat corruption or process lock.

my_file = open("targets.txt","r")
my_file.read()
print(my_file)
my_file.close()

The open() function takes 2 arguments: the actual filename and its mode.

You can use the + symbol to modify the mode as you can see.

The with() and open() statements

Using the open() function with with().

with open("targets.txt","r") as target_file:
    file_content = target_file.read()
    print(file_content)

You'd notice that Python has 2 functions for reading from a file, read() and readline().

read() reads the content from the file, all at once. readline() read the content from the file line by line. This make readline great for working with loops.

We use .read() to read the content of a file, so we use.........write() to write content to a file.

The write() function

The write() function is part of the built-in file object in Python. To write to a file is just as simple as reading from the the file.

First we set the file in the write mode and simply pass the data we want to write to it.

message = "Message in a bottle"
with open("file.txt","w") as f:
    f.write(message)
    f.close()

In this example, we set the file mode to "write only". This means that if the file already exists with content, it will be overwritten.

It's a good idea to use the "append" or "a" option for writing to files and it just adds the new data to the end of the file.

Relative File Paths

A relative file path tell Python to look for a given location relative to the directory where the currently running program file is stored.

For example, your Python project is in python_projects/ and the text file is in a sub-directory text_files/ within the Python project, then relative path would be 'text_files/file1.txt'.

Absolute File Paths

The absolute file path is the exact location of the file on your computers hard drive.

Using the same example from the relative file path, the absolute file path will something like this: 'C:/Users/User1/Documents/python_projects/text_files/file1.txt'.

Keeping with the theme of "batteries included", Python also as a few third-party / external modules for file handling and these are:

• the os module
• the pathlib module

These modules do more or less the same thing, provides python access to the controls for working with directories and files (no the creation of the files however), with their major difference being that one provides a lower level access (os module) and the other providing a more abstracted, high-level access (pathlib).

In your development journey, you usually find yourself using both pathlib and os modules.

Reading a file

from pathlib import Path

path = Path('targets.txt')
contents = path.read_text()
print(contents)

Writing a file

from pathlib import Path

path = Path('targets.txt')
path.write_text("192.168.1.1")

With the above example, if there is already content in the targets.txt file, it will be overwritten. The easiest way to deal with this is to read the content first and append the new data to it.

from pathlib import Path

path = Path("targets.txt")
read_data = path.read_text()

if read_data:
    read_data += "10.10.1.1\n"
    read_data += "172.16.23.2\n"
    path.write_text(read_data)
else:
    data = "10.10.1.1\n"
    data += "172.16.23.2\n"
    path.write_text(data)

Get the system default home directory

from pathlib import Path

print(f"Default path: {Path.home}")

Get the current working document

from pathlib import Path

print(Path.cwd())

The os modules help you as a programmer by providing a portable way of using operating system dependant functionality.

This module gives us options to manipulate file paths, make directories, and other operating system specific actions such as getting environment details, getting logged on user profile, etc.

Some key options to be aware of

Get OS name

Let's use the os module to get the os that the program is running on:

import os

if os.name == "nt":
    print("Current OS: Windows")
else:
    print("Current OS: Linux")

Get the list of directories

Now let's get the list of directoies in a folder

import os

total_listing = os.scandir()
print(total_listing)