Big File UploadΒΆ

To handle big files without using all the available memory a generator can be used. The generator will return the file in small chunks:

#!/usr/bin/env python
import cgi, os
import cgitb; cgitb.enable()

try: # Windows needs stdio set for binary mode.
    import msvcrt
    msvcrt.setmode (0, os.O_BINARY) # stdin  = 0
    msvcrt.setmode (1, os.O_BINARY) # stdout = 1
except ImportError:

form = cgi.FieldStorage()

# Generator to buffer file chunks
def fbuffer(f, chunk_size=10000):
    while True:
        chunk =
        if not chunk: break
        yield chunk

# A nested FieldStorage instance holds the file
fileitem = form['file']

# 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)
    f = open('files/' + fn, 'wb', 10000)

    # Read the file in chunks
    for chunk in fbuffer(fileitem.file):
    message = 'The file "' + fn + '" was uploaded successfully'

    message = 'No file was uploaded'

print """\
Content-Type: text/html\n
""" % (message,)