CSV Basics

CSV (comma-separated values) is the universal export format of spreadsheets.

line = "minh,21,Hanoi"
name, age, city = line.split(",")
# "minh", "21", "Hanoi"  — note age is still a STRING

Reading a whole CSV:

rows = []
with open("people.csv", encoding="utf-8") as f:
    for line in f:
        rows.append(line.strip().split(","))

The first row of most CSVs is a header — skip it with slicing (rows[1:]) or read it as column names. Values always arrive as strings; convert numbers yourself.

Writing is the mirror image:

with open("summary.csv", "w", encoding="utf-8") as f:
    f.write("name,total\n")
    f.write(f"{name},{total}\n")

(The real csv module handles quoting edge cases — meet it in Intermediate. For well-behaved data, split/join is honest work.)