Understanding the Issue with Mac-formatted CSV Files in Django

The issue you're experiencing with sample-mac.csv is likely related to how Django's InMemoryUploadedFile.chunks() method handles different line endings, particularly the old Macintosh convention that uses \r (carriage return) as the line ending character.

Line Ending Handling in Django

According to the Django documentation, when iterating over uploaded files, Django uses universal newlines to split lines. The following are recognized as ending a line:

• Unix end-of-line convention: \n
• Windows convention: \r\n
• Old Macintosh convention: \r

However, when you're using the chunks() method, you're getting raw binary data chunks rather than using Django's line iteration functionality. This means you're bypassing the universal newline handling that Django would normally apply when iterating over the file directly.

Potential Solutions

1. Iterate Over the File Directly

Instead of using chunks(), try iterating over the file directly to leverage Django's universal newline handling:

PYTHONCopied
for line in file:
    # Django will handle the \r line endings properly here
    print(line)

2. Pre-process the Binary Data

If you need to continue using chunks(), you could pre-process the binary data to handle the Mac-style line endings:

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sampler = next(chunks)
# Replace Mac-style line endings with Unix-style before decoding
sampler = sampler.replace(b'\r', b'\n')
print(sampler.decode(charset))

3. Use the io Module with Universal Newlines

You could also wrap the file object with Python's io module to handle universal newlines:

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import io

# Create a TextIOWrapper with universal newline support
text_file = io.TextIOWrapper(file, encoding=charset or 'utf-8', newline=None)
content = text_file.read()
print(content)

Why Direct File Reading Works

When you open the file directly with open("sample-mac.csv", "r"), Python's built-in file handling automatically deals with the different line ending styles, especially if you're on a modern system where universal newline support is enabled by default.

The chunks() method, on the other hand, is designed for efficient binary data handling and doesn't apply the same text processing that would normalize line endings.

This difference in handling explains why the direct file reading works correctly while the chunks() method produces unexpected results with Mac-formatted files.