Lecture 7 : File Input/Output in Python

File I/O Fundamentals
📌 File I/O (Input/Output) in Python involves operations like opening, reading, writing, updating, and deleting files.
💾 Data persistence for information that must remain after the system shuts down is achieved by storing it in files, unlike volatile RAM storage.
📝 Files are broadly categorized into Text Files (storing data as characters, e.g., `.txt`, `.docx`) and Binary Files (storing data in non-character formats, e.g., `.mp4`, `.png`).

Opening and Accessing Files
🔑 Files are opened using the `open()` function, which requires the file name (path) and a mode as parameters.
🛠️ The default mode is 'r' (read); if no mode is specified, Python assumes reading.
🛑 A key practice is to close the file using `f.close()` after operations to prevent data corruption or unauthorized access, although the `with` statement handles this automatically.

File Reading Methods
📖 The primary methods for reading data are `f.read()` (reads the entire file content as a single string), `f.read(N)` (reads the first N characters), and `f.readline()` (reads one line at a time).
➡️ When using `f.read()`, the file pointer moves to the end, meaning subsequent `readline()` calls will return empty strings unless the file is reopened.
➡️ `f.readline()` is useful for processing files line-by-line, returning an empty string when the end of the file is reached.

File Writing and Modification Modes
✍️ Writing operations use modes like 'w' (write), which overwrites existing content, and 'a' (append), which adds new data to the end of the file.
🆕 Both 'w' and 'a' modes will create the file if it does not already exist.
➡️ To ensure data appears on new lines, the newline character `\n` must be explicitly included when writing or appending data.

Advanced File Modes and the `with` Statement
➕ Compound modes like 'r+' (read and write) allow simultaneous operations; 'r+' positions the pointer at the beginning and allows overwriting from the start.
➕ 'w+' (write and read) truncates the file (clears all content) upon opening, and the pointer starts at the beginning.
➕ 'a+' (append and read) positions the pointer at the end for appending, but reading can still occur after seeking or reading from the start.
🔒 The `with open(...) as f:` syntax is the preferred method as it automatically handles closing the file, even if errors occur within the block.

Deleting Files
🗑️ Deleting a file requires importing the `os` module and using the `os.remove('filename')` function.
📦 Modules like `os` are pre-installed libraries containing useful functions; external modules (like TensorFlow) may require installation via `pip install module_name`.

Key Points & Insights
➡️ Prioritize the `with` statement for file handling to ensure files are automatically and safely closed, avoiding manual calls to `f.close()`.
➡️ When reading sequentially, remember that `f.read()` consumes the entire file, rendering subsequent `readline()` calls ineffective until the file is reset or reopened.
➡️ To replace text within a file, the safest process is to Read $\rightarrow$ Modify in memory $\rightarrow$ Overwrite (Write) the entire content back to the file.
➡️ For line-by-line processing where the word location is needed, use `f.readline()` within a `while` loop, tracking the line number, and returning immediately upon finding the first match.

📸 Video summarized with SummaryTube.com on Feb 09, 2026, 02:21 UTC