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File Upload Example in Python
File upload in Python can be implemented using the CGI (Common Gateway Interface) environment. This involves creating an HTML form for file selection and a Python script to handle the server−side file processing.
The file upload process consists of two main components: an HTML form that allows users to select files, and a Python CGI script that processes and saves the uploaded files to the server.
Creating HTML Form for File Upload
The HTML form uses <input type="file"> to create a file selection field and <input type="submit"> for the upload button. The form must include enctype="multipart/form-data" to handle file uploads properly ?
Example
<!DOCTYPE html>
<html>
<body>
<form enctype="multipart/form-data" action="save_file.py" method="post">
<p>File: <input type="file" name="filename" /></p>
<p><input type="submit" value="Upload" /></p>
</form>
</body>
</html>
Output
Python Script to Handle File Upload
The Python CGI script processes the uploaded file using the cgi module. Key components include ?
- cgitb.enable() − Activates error reporting for debugging
- cgi.FieldStorage() − Provides access to form data and uploaded files
- os.path.basename() − Prevents directory traversal attacks
Example
#!/usr/bin/env python3
# Importing required modules
import cgi
import os
import cgitb
# Enable CGI error reporting
cgitb.enable()
# Create instance of FieldStorage
form = cgi.FieldStorage()
# Get the file item from the form
fileitem = form['filename']
# Test if the file was uploaded
if fileitem.filename:
# Strip leading path from file name to avoid directory traversal attacks
fn = os.path.basename(fileitem.filename)
# Open the file and write its contents to the server
with open('/tmp/' + fn, 'wb') as f:
f.write(fileitem.file.read())
# Success message
message = f'The file "{fn}" was uploaded successfully'
else:
# Error message
message = 'No file was uploaded'
# Print the HTTP headers and HTML content
print(f"""\
Content-Type: text/html\n
<html>
<body>
<p>{message}</p>
</body>
</html>
""")
Output Examples
When a file is uploaded successfully ?
The file "document.txt" was uploaded successfully
When no file is selected ?
No file was uploaded
Security Considerations
Always use os.path.basename() to prevent directory traversal attacks. Consider implementing file type validation and size limits for production applications.
Conclusion
File uploads in Python using CGI require an HTML form with proper encoding and a Python script using the cgi module. Always implement security measures like path sanitization and file validation for safe file handling.
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