Reading and Writing Text Files

Variables live in the computer’s memory and vanish when the program ends. To keep data for a long time, we have to write it to a file. A text file is a file that holds plain text (for example notes.txt) and can be opened in any editor. Python works with files through the open() function.

Working with a file has three stages: open, read or write, close. The most convenient way is the with construction: with open("notes.txt", "w", encoding="utf-8") as f: and inside it f.write("Salom\n"). When the block ends, the file closes itself. The mode letter matters: "r" is reading, "w" is writing (old content is erased), "a" is appending to the end.

There are several ways to read a file. f.read() returns the whole text as one string, f.readline() reads one line, and f.readlines() returns a list of lines. The simplest way is to loop over the file: for line in f: and print(line.strip()). The strip() method removes the invisible newline character at the end.

If the file being read does not exist, Python raises a FileNotFoundError. It can be caught with try and except FileNotFoundError: to show the user a clear message. Make it a habit to give encoding="utf-8" so that Uzbek letters are saved correctly. When writing numbers to a file, convert them to strings with str().

Key takeaways

• Data written to a file is kept even after the program ends.
• with open(name, mode, encoding="utf-8") as f: is a convenient way to work with a file.
• Modes: "r" read, "w" write, "a" append.
• A missing file raises FileNotFoundError; it can be caught with try/except.