Welcome to the first lesson in our course on "Fundamentals of Text Data Manipulation". This lesson will introduce you to the crucial skill of reading text files in Python. Text files are a fundamental data source in programming, commonly used for storing data, configuration files, and logs. Being able to open and read files in Python is a foundational skill you'll often rely on when working with data. By the end of this lesson, you will be able to read the entire contents of a text file into a string, a skill essential for various data manipulation tasks. Let's get started!

A file path is essentially the address of a file in your system's storage. It tells your program where to find or save a file. There are two types of file paths:

• Absolute Path: This is the full path to a file, starting from the root directory. Here are some examples from different operating systems:

  • Linux: /home/user/documents/input.txt
  • Mac: /Users/user/documents/input.txt
  • Windows: C:\Users\user\documents\input.txt

• Relative Path: This path is relative to the directory you are working in. For example, documents/input.txt assumes your script is running from the user directory in the examples above.

Here's how you can specify a file path in Python:

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1file_path = 'input.txt'  # Relative path

Make sure your Python script and the text file are in the same directory if you use a relative path. Otherwise, use the absolute path to ensure that Python can find your file. In the CodeSignal environment, your Python file will always be in the same directory with a file or a directory where the file is. This means you can always use a relative path in CodeSignal.

When working with relative paths, it's important to understand the structure of your directories. Here are a few examples with file trees:

1. Example 1:

   File Tree:

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   1project/
   2├── script.py
   3└── data/
   4    └── input.txt

   Relative Path:

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   1file_path = 'data/input.txt'

2. Example 2:

   File Tree:

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   1user/
   2├── documents/
   3│   └── script.py
   4└── input.txt

   Relative Path:

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   1file_path = '../input.txt'

The .. is used to navigate to the parent directory. It works this way in both MacOs/Linux and Windows.

1. Example 3:

   File Tree:

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   1application/
   2├── scripts/
   3│   ├── script1.py
   4│   └── script2.py
   5└── resources/
   6    └── input.txt

   Relative Path (assuming the script is in script2.py):

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   1file_path = '../resources/input.txt'

These examples illustrate how relative paths depend on the current working directory of your script.

In Python, the open() function is used to open a file. This function requires the file path and the mode you want to open the file in. By default, the open() function applies the read mode 'r'.

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1file_path = 'input.txt'
2file = open(file_path)  # 'r' is implicit here

In this code snippet, file is a variable that holds a file object. This object acts as a handle to work with the file you've opened.

Once you've opened a file, you can read its contents using the read() method.

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1file_path = 'input.txt'
2file = open(file_path)
3
4content = file.read()
5print("Full file content:")
6print(content)

Here, content stores the entire contents of the file as a string, which you can then process or display.

It's critical to close a file after you've finished working with it. This frees up system resources and ensures that no more operations can be performed on the file inadvertently.

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1file.close()

By calling file.close(), you ensure that the file is properly closed, which is essential for good resource management.

The with statement simplifies file handling by automatically closing the file once the block of code is executed, even if an error occurs.

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1file_path = 'input.txt'
2with open(file_path, 'r') as file:
3    content = file.read()
4print("Full file content:")
5print(content)

• Using with open(file_path, 'r') as file: ensures that once the block inside the with statement is exited, the file is automatically closed.
• This pattern prevents resource leaks, which can happen if many files are left open, potentially exhausting system resources.

In this lesson, you've learned how to:

• Specify file paths correctly with examples from different operating systems.
• Use Python's open() function in read mode to open a file and handle the file object.
• Read the contents of a file.
• Close a file manually to manage resources.
• Use the with statement to automatically close files and manage resources effectively.
• Define relative paths correctly with examples and file tree illustrations.

These foundational skills will serve you well in handling data stored in text files. As you move on to the practice exercises, you'll apply these concepts by reading different text files and extracting their content. This hands-on experience will solidify your understanding, preparing you for more advanced file manipulation techniques in the future. Keep up the good work, and happy coding!