CSV Files with the csv Module

CSV Files with the csv Module

A CSV (comma-separated values) file is a text file in which every line is a record and commas separate its fields. The csv module reads and writes them correctly, including fields that themselves contain a comma (those are put in quotes).

import csv

with open("marks.csv", "w", newline="") as f:
    w = csv.writer(f)
    w.writerow(["Roll", "Name", "Marks"])            # one record
    w.writerows([[1, "Asha", 88], [2, "Ravi", 72]])  # many records

with open("marks.csv", newline="") as f:
    for row in csv.reader(f):
        print(row)        # ['Roll', 'Name', 'Marks'], ['1', 'Asha', '88'], ...

• Open CSV files with newline="". Otherwise the writer's own line endings get an extra blank line on Windows.
• csv.reader gives each record as a list of strings: convert numbers with int().
• The first row is often a header; skip it with next(reader).
• csv.writer(f, delimiter="|") uses another separator.

import csv
import sys

reader = csv.reader(sys.stdin)   # stands in for csv.reader(open("marks.csv", newline=""))
marks = []
for row in reader:
    pass  # skip the header; collect the marks; print names above 75
print(f"Average: {sum(marks) / max(len(marks), 1):.1f}")