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Practice

CSV File Parsing

CSV (Comma-Separated Values) files are widely used for storing tabular data, such as spreadsheets or simple databases.

Python’s built-in csv module provides convenient tools for reading and writing CSV files.

Note: The Python practice environment doesn’t support importing files from your local machine. The examples below are for demonstration purposes only.


1. Reading a CSV File​

Use csv.reader() to read rows from a CSV file one at a time.

Reading a CSV File
import csv

with open("people.csv", newline="") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)
  • Each row is a list of values (split by commas).
  • newline="" avoids issues with extra blank lines on Windows.

2. Writing to a CSV File​

Use csv.writer() to create and write rows to a CSV file.

Writing to a CSV File
import csv

with open("new_people.csv", "w", newline="") as file:
    writer = csv.writer(file)
    writer.writerow(["Name", "Age"])
    writer.writerow(["Alice", 28])
    writer.writerow(["Bob", 34])
  • writerow() writes a list as one row in the file.
  • First row usually contains headers.

3. Reading as Dictionaries​

csv.DictReader() reads each row as a dictionary, making it easier to work with named columns.

Reading as Dictionaries
import csv

with open("people.csv", newline="") as file:
    reader = csv.DictReader(file)
    for row in reader:
        print(row["Name"], "is", row["Age"], "years old.")
  • You can access columns by their header names like "Name" and "Age".

Summary​

FunctionDescription
csv.reader()Reads CSV rows as lists
csv.writer()Writes rows to a CSV file
csv.DictReader()Reads rows as dictionaries

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