Python Tips: the tempfile library
The other day I was writing a python test, and I needed a temporary directory and file.
Normally, I make these tests happen with os and pathlib libraries.
It works well enough, and therefore I never had reason to change it.
However, this time I asked Claude for a quick test that I was going to edit after, and it showed me the tempfile
library.
This module creates temporary files and directories. It works on all supported platforms. TemporaryFile, NamedTemporaryFile, TemporaryDirectory, and SpooledTemporaryFile are high-level interfaces which provide automatic cleanup and can be used as context managers. mkstemp() and mkdtemp() are lower-level functions which require manual cleanup.
You can do things like this:
with tempfile.NamedTemporaryFile(mode='w+', delete=True) as temp_file:
# You can write data to the temporary temp_file
# `data` can just be a string of your liking, like a fake CSV
temp_file.write(data)
print(f"Created temporary file: {temp_file.name}")
# You can then process the file via it's path
# or just process it's content
# ...
So practical! Quick tip of the day! Here’s a basic complete example:
import pandas as pd
import tempfile
import os
import unittest
def read_csv_to_dataframe(file_path):
if not os.path.exists(file_path):
raise FileNotFoundError(f"File not found: {file_path}")
return pd.read_csv(file_path)
class TestCSVReader(unittest.TestCase):
def test_read_csv_to_dataframe(self):
"""Test that CSV data is correctly loaded into a DataFrame."""
# Create sample CSV data
csv_data = """name,age,city
Alice,32,Seattle
Bob,45,Portland
Charlie,28,San Francisco"""
# Create a temporary CSV file
with tempfile.NamedTemporaryFile(mode='w+', suffix='.csv') as temp_file:
# Write the CSV data
temp_file.write(csv_data)
temp_file.flush()
temp_path = temp_file.name
# Test the function
df = read_csv_to_dataframe(temp_path)
# Verify the results
self.assertEqual(len(df), 3)
self.assertEqual(list(df.columns), ['name', 'age', 'city'])
self.assertEqual(df.iloc[0]['name'], 'Alice')
self.assertEqual(df.iloc[1]['age'], 45)
self.assertEqual(df.iloc[2]['city'], 'San Francisco')
if __name__ == "__main__":
unittest.main()