Saving to PNG, SVG, PDF in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What file is created by this code?

Consider this Python code using matplotlib:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('chart.svg')

What type of file will be saved?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('chart.svg')

A An SVG vector graphic file named 'chart.svg'

B A PNG image file named 'chart.svg'

C A PDF document named 'chart.svg'

D A text file named 'chart.svg'

💡 Hint

The file extension determines the format matplotlib saves.

The 'savefig' function saves the plot in the format matching the file extension. Here, '.svg' means a vector graphic SVG file.

❓ Predict Output

intermediate

What happens if you save a plot with dpi=300 to PNG?

Look at this code:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('high_res.png', dpi=300)

What is the effect of dpi=300?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('high_res.png', dpi=300)

A The saved PNG image will be smaller in file size

B The saved PNG image will have higher resolution and be sharper

C The saved PNG image will be in vector format

D The dpi parameter is ignored for PNG files

💡 Hint

DPI means dots per inch, affecting image clarity.

Setting dpi=300 increases the pixel density, making the PNG image sharper and suitable for printing.

🔧 Debug

advanced

Why does this PDF save fail?

This code tries to save a plot as PDF but fails:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('plot.pdf', format='png')

Why does it fail to save a PDF file?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.savefig('plot.pdf', format='png')

A The format argument conflicts with the file extension, causing a mismatch error

B Matplotlib cannot save PDF files

C The file name must be 'plot.png' to save as PNG

D The plot must be shown before saving

💡 Hint

Check if the format matches the file extension.

The 'format' parameter says save as PNG but the file extension is '.pdf'. This mismatch causes an error or unexpected behavior.

❓ data_output

advanced

How many files are created by this code?

Given this code:

import matplotlib.pyplot as plt
for ext in ['png', 'svg', 'pdf']:
    plt.plot([1, 2], [3, 4])
    plt.savefig(f'file.{ext}')
    plt.clf()

How many files are created after running this code?

Matplotlib

import matplotlib.pyplot as plt
for ext in ['png', 'svg', 'pdf']:
    plt.plot([1, 2], [3, 4])
    plt.savefig(f'file.{ext}')
    plt.clf()

A 1 file

B 2 files

C 3 files

D 0 files

💡 Hint

Each loop iteration saves one file with a different extension.

The loop runs 3 times, saving 'file.png', 'file.svg', and 'file.pdf'. So 3 files are created.

🚀 Application

expert

Choose the best code to save a plot as a high-quality PDF with transparent background

You want to save a matplotlib plot as a PDF file named 'output.pdf'. The PDF should have a transparent background and high quality. Which code snippet achieves this?

A plt.savefig('output.pdf', transparent=True, dpi=72)

B plt.savefig('output.pdf', transparent=False, dpi=72)

C plt.savefig('output.pdf', transparent=False, dpi=300)

D plt.savefig('output.pdf', transparent=True, dpi=300)

💡 Hint

Transparent background requires transparent=True. Higher dpi means better quality.

Setting transparent=True makes the background clear. dpi=300 increases quality. This combination saves a high-quality transparent PDF.