Day 27: with Statement and CSV

Quick Answer

What You Will Learn

• csv.writer writes rows in CSV format.
• newline="" is required when opening CSV files, or extra blank lines appear.
• csv.DictReader turns each row into a dict, so values are read by column name (r["amt"]).
• sum(...) totals all amounts: in the example the total is 35.
• with closes the file or buffer itself, so forgetting close() is no longer a risk.

Code

import csv, io
buf = io.StringIO()
rows = [["item", "amt"], ["tea", 20], ["coffee", 15]]
with io.StringIO() as out:
    pass
writer = csv.writer(buf)
writer.writerows(rows)
buf.seek(0)
with io.StringIO(buf.getvalue(), newline="") as f:
    total = sum(int(r["amt"]) for r in csv.DictReader(f))
print(total)
print(buf.getvalue())

Output

35
item,amt
tea,20
coffee,15

Code Explained, Line by Line

1. csv.writer writes rows in CSV format.
2. newline="" is required when opening CSV files, or extra blank lines appear.
3. csv.DictReader turns each row into a dict, so values are read by column name (r["amt"]).
4. sum(...) totals all amounts: in the example the total is 35.
5. with closes the file or buffer itself, so forgetting close() is no longer a risk.

Real-Life Use

Spreadsheets, reports and exported data are CSV files in almost every business.

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