Writing to CSV with to_csv in Pandas - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the content of the CSV file after running this code?

Consider the following Python code using pandas to write a DataFrame to a CSV file. What will be the content of the CSV file?

Pandas

import pandas as pd

df = pd.DataFrame({'Name': ['Alice', 'Bob'], 'Age': [25, 30]})
df.to_csv('output.csv', index=False)

A "Name;Age\nAlice;25\nBob;30\n"

B ",Name,Age\n0,Alice,25\n1,Bob,30\n"

C "Name,Age\n0,Alice,25\n1,Bob,30\n"

D "Name,Age\nAlice,25\nBob,30\n"

💡 Hint

Check the index parameter in to_csv and the default separator.

Since index=False, the row numbers are not saved. The default separator is a comma, so the CSV content has columns Name and Age separated by commas.

❓ data_output

intermediate

How many rows will the CSV file contain after this code runs?

This code writes a DataFrame to a CSV file. How many rows (including header) will the CSV file have?

Pandas

import pandas as pd

df = pd.DataFrame({'City': ['NY', 'LA', 'Chicago'], 'Population': [8000000, 4000000, 2700000]})
df.to_csv('cities.csv', index=True)

A 3

B 4

C 5

D 2

💡 Hint

Remember that index=True adds an index column and the header row is also counted.

The DataFrame has 3 rows. With index=True, the index is saved as a column. The CSV includes a header row, so total rows = 3 data rows + 1 header = 4.

🔧 Debug

advanced

What error does this code raise when writing to CSV?

Look at this code snippet. What error will it raise when executed?

Pandas

import pandas as pd

df = pd.DataFrame({'A': [1, 2], 'B': [3, 4]})
df.to_csv('data.csv', sep=';')
df.to_csv('data.csv', sep=',', header=False, index=False, mode='x')

A FileExistsError

B ValueError

C No error, runs successfully

D TypeError

💡 Hint

Check the meaning of mode='x' when opening files.

The first to_csv creates 'data.csv'. The second call uses mode='x', which tries to create a new file but fails if the file exists, raising FileExistsError.

🚀 Application

advanced

Which option correctly writes a DataFrame to CSV with tab separator and no header?

You want to save a DataFrame to a CSV file using a tab character as separator and without writing the header row. Which code does this correctly?

Pandas

import pandas as pd

df = pd.DataFrame({'X': [10, 20], 'Y': [30, 40]})

A df.to_csv('file.tsv', sep='\t', header=False)

B df.to_csv('file.tsv', sep='\t', index=False, header=True)

C df.to_csv('file.tsv', sep='\t', header=False, index=True)

D df.to_csv('file.tsv', sep='\t', index=False)

💡 Hint

Check the parameters sep and header in to_csv.

Option A sets sep='\t' for tab separator and header=False to omit the header row. This matches the requirement exactly.

🧠 Conceptual

expert

What is the effect of using line_terminator='\r\n' in to_csv?

When writing a CSV file with pandas to_csv, what does setting line_terminator='\r\n' do?

A It adds extra blank lines between rows in the CSV file.

B It causes an error because <code>line_terminator</code> only accepts single characters.

C It changes the line ending to Windows style CRLF instead of the default LF.

D It removes all line breaks, writing the CSV as a single line.

💡 Hint

Think about different operating systems and their line ending conventions.

Windows uses carriage return + line feed (\r\n) as line endings. Setting line_terminator='\r\n' makes the CSV use Windows-style line breaks instead of the default Unix-style \n.