How do you manipulate CSV files using python?

Question 1

What does CSV stand for?

Answer 1

Comma-Separated Values. It’s a plain text format where data is organized in rows, with values in each row separated by a delimiter (like a comma).

Question 2

What is the built-in Python module for handling CSVs?

Answer 2

The csv module. (import csv)

Question 3

csv: How do you open a CSV file for reading?

Answer 3

Use with open(‘filename.csv’, mode=’r’) as file:

Question 4

csv: What object do you create to read the file row by row?

Answer 4

A csv.reader object: \ncsv_reader = csv.reader(file)

Question 5

csv: When iterating over a csv.reader, what data type is each row?

Answer 5

A list of strings.

Question 6

csv: How do you read a CSV file where the first row is a header?

Answer 6

Use csv.DictReader. Each row will be a dictionary where keys are the header names.

Question 7

csv: When opening a file for writing with the csv module, what two arguments are crucial?

Answer 7

mode=’w’ (to write) and newline=’’ (to prevent blank lines between rows on Windows).

Question 8

csv: What object do you create to write to a CSV file?

Answer 8

A csv.writer object: \ncsv_writer = csv.writer(file)

Question 9

csv: How do you write a single row of data (as a list)?

Answer 9

csv_writer.writerow([‘data1’, ‘data2’, ‘data3’])

Question 10

csv: How do you write multiple rows at once (from a list of lists)?

Answer 10

csv_writer.writerows(list_of_lists)

Question 11

csv: How do you specify a different delimiter (like a semicolon)?

Answer 11

Pass it as an argument: \ncsv.reader(file, delimiter=’;’)

Question 12

What is the most popular third-party library for CSV manipulation, especially for data analysis?

Answer 12

The pandas library.

Question 13

pandas: How do you read a CSV file into a DataFrame?

Answer 13

import pandas as pd \ndf = pd.read_csv(‘filename.csv’)

Question 14

pandas: What is a DataFrame?

Answer 14

A 2D labeled data structure, like a spreadsheet or SQL table, with columns and rows.

Question 15

pandas: How do you access a single column (a “Series”) from a DataFrame?

Answer 15

df[‘column_name’]

Question 16

pandas: How do you filter rows (e.g., all rows where ‘age’ > 30)?

Answer 16

df[df[‘age’] > 30]

Question 17

pandas: How do you add a new column to the DataFrame?

Answer 17

df[‘new_column_name’] = [value1, value2, …]

Question 18

pandas: How do you save a DataFrame back to a new CSV file?

Answer 18

df.to_csv(‘new_file.csv’)

Question 19

pandas: When using to_csv(), how do you prevent it from saving the DataFrame’s row numbers (the index)?

Answer 19

df.to_csv(‘new_file.csv’, index=False)