CSV File Handling

Work with comma-separated data, like a simple spreadsheet.

A CSV file (comma-separated values) stores rows of data, with commas between the fields. It is the plain-text cousin of a spreadsheet.

What a CSV looks like

students.csv

Ava,15,Blue
Ben,14,Green
Cara,16,Red

Each line is one record; each value is separated by a comma. Here the fields are name, age and favourite colour.

Writing a CSV

write.py

file = open("students.csv", "w")
file.write("Ava,15,Blue\n")
file.write("Ben,14,Green\n")
file.write("Cara,16,Red\n")
file.close()

How it works

A CSV is just a text file, so we use the same open, write and close.
Put commas between the fields and \n at the end of each record.

Reading and splitting each line

read.py

file = open("students.csv", "r")
for line in file:
    line = line.strip()
    fields = line.split(",")
    print(fields[0], "is", fields[1], "years old")
file.close()

Output

Ava is 15 years old
Ben is 14 years old
Cara is 16 years old

How it works

We read the file one line at a time.
.strip() removes the newline from the end of the line.
.split(",") breaks the line into a list of fields at each comma.
fields[0] is the first value, fields[1] the second, and so on.

Fields are an arraysplit(",") gives you a 1-D array of the fields, so everything you learned about arrays applies here.

Everything read is textEvery field read from a file is a string. Cast with int(fields[1]) if you need to do maths with it.

The CSV recipeReading a CSV is 'read a line, strip it, split it on commas' — then use the fields by index.

What you have learned

A CSV stores records, one per line, with commas between fields.
It is an ordinary text file, so open, write and close still apply.
.split(",") turns a line into a list of fields.
Fields are text — cast them if you need numbers.