Programming with Python - Files

Chapter 12 - Files

How to open a file for reading in Python

Use open("filename.txt","r"); raises FileNotFoundError if missing.

What the read() method does

Reads entire file as one string.

What readline() does

Reads one line at a time.

What readlines() returns

List of all lines in the file.

How iterating over a file works

Reads one line per loop, very memory-efficient.

Why newline characters appear

Lines include "\n"; remove with rstrip().

How Python behaves at EOF

read() returns "" and iteration stops.

Why files must be closed

Releases system resources and prevents data issues.

How to open a file for writing

Use open("file.txt","w") to overwrite or "a" to append.

How to write text to a file

Use write(); convert numbers to strings.

Why file output is buffered

Writes may be delayed; flush() forces writing.

Why closing a file after writing matters

Ensures all buffered data is saved.

What os.stat() is used for

Gets file metadata like size and timestamps.

How to delete a file

Use os.remove("filename.txt").

Why os.path.join() is recommended

Creates correct paths on any OS.

Useful os.path functions

exists(), isfile(), isdir(), getsize(), split(), sep.

What os.walk() does

Traverses directories and lists folders/files.

Difference between binary and text files

Text stores characters; binary stores raw bytes.

How to read a binary file

Open with "rb" and use read().

What a bytes object represents

Immutable sequence of byte values 0–255.

Ways to create bytes objects

From strings, lists, literals, or hex escapes.

Purpose of the struct module

Packs/unpacks binary data with format codes.

What endianness means

">" = big-endian, "<" = little-endian.

Why the with statement is used

Automatically closes files even on errors.

How to read a file with with

Use with open(...) as f: to ensure safe closing.

Why with is preferred

Avoids leaks and makes code cleaner.

What a CSV file is

Common table-like format using commas.

How to read a CSV file

Use csv.reader; rows come as lists of strings.

Why CSV values need type conversion

Reader returns strings; convert manually.

How to read CSV with custom delimiter

Use csv.reader(..., delimiter=";").

How to write CSV files

Use csv.writer with writerow() or writerows(); newline="" on Windows.