File I/O

Files store data persistently. Variables in memory disappear when a program ends, but data written to a file can remain. File I/O means input from files and output to files.

💾 File Persistent text　⇄　🐍 Python program Read input, process it, and write results

open() and file modes

open() returns a file object. Reading, writing, and closing happen through that object.

file = open("text.txt", "r", encoding="UTF-8")
content = file.read()
file.close()

Prefer with open(...) as file, which closes the file automatically after the block. Explicit encoding="UTF-8" also avoids mismatched system defaults.

with open("text.txt", "r", encoding="UTF-8") as file:
    content = file.read()

Reading methods

• read(): read everything into one string.
• readline(): read one line.
• readlines(): return all lines as a list of strings.
• Iterate over the file object to process one line at a time, useful for larger files.

Parsing words

The following program reads quotes.txt, strips English punctuation, and writes every word to words.txt. The two files may share one with statement or use nested with blocks.

import string

with open("words.txt", "w", encoding="UTF-8") as output_file:
    with open("quotes.txt", "r", encoding="UTF-8") as input_file:
        for line in input_file:
            for word in line.split():
                word = word.strip(string.punctuation)
                output_file.write(word + "\n")