Python 3.6 Zipfile Backport

Warnings

• breaking Pickling `zipfile.ZipFile` instances will raise a `TypeError` in Python 3.6+ (and by extension, when using `zipfile36`). This behavior change fixed a prior bug in Python < 3.6 where `ZipFile` objects containing unpicklable `_thread.RLock` objects were incorrectly picklable. Code relying on pickling `ZipFile` objects for serialization will break.
  Fix: Avoid pickling `zipfile.ZipFile` instances directly. Instead, serialize the necessary file paths or contents and recreate `ZipFile` objects as needed.
• gotcha The `zipfile.is_zipfile()` function is not a robust file type identifier and can produce false positives. It primarily checks for the presence of a ZIP central directory signature at the end of a file, which can coincidentally appear in other file types (e.g., gzipped files, executables with appended data).
  Fix: For reliable file type detection, use dedicated file-sniffing libraries (e.g., `python-magic`, `filetype`) or validate the content more thoroughly after initial checks, especially when dealing with untrusted sources.
• breaking Error types for certain operations changed in Python 3.6. Specifically, operations on a closed `ZipFile` (e.g., `open()`, `write()`, `extract()`, `extractall()`, `writestr()`) or with an invalid mode will now raise `ValueError` instead of `RuntimeError`.
  Fix: Update exception handling blocks to catch `ValueError` instead of `RuntimeError` for operations that misuse `ZipFile` objects (e.g., operating on a closed archive).
• deprecated The `mode='U'` option for `ZipFile.open()` (for universal newlines mode) was removed in Python 3.6.
  Fix: Instead of `mode='U'`, use `io.TextIOWrapper` to read compressed text files with explicit encoding and newline handling. For example: `io.TextIOWrapper(zip_file.open('member.txt'), encoding='utf-8', newline='')`.

Install

• pip install zipfile36 Install `zipfile36`

Imports

• zipfile

  import sys
  if sys.version_info >= (3, 6):
      import zipfile
  else:
      import zipfile36 as zipfile

  The backport is designed to be aliased as `zipfile` for compatibility with existing code written for the standard library's `zipfile` module. Direct import as `zipfile36` works but deviates from the intended usage pattern.

Quickstart

This quickstart demonstrates how to use `zipfile36` (aliased as `zipfile`) to create a ZIP archive, add a file to it, and then read the file's contents from the archive. It includes the recommended conditional import statement.

import sys
import os
import io

# Suggested usage for zipfile36 backport
if sys.version_info >= (3, 6):
    import zipfile
else:
    try:
        import zipfile36 as zipfile
    except ImportError:
        print("zipfile36 not installed. Please install with 'pip install zipfile36' for Python versions < 3.6.")
        sys.exit(1)

# Create a dummy file
file_content = "Hello, zipfile36! This is a test file."
file_name = "test_file.txt"
with open(file_name, "w") as f:
    f.write(file_content)

zip_file_name = "my_archive.zip"

# 1. Create a zip archive and add a file
print(f"Creating '{zip_file_name}' and adding '{file_name}'...")
with zipfile.ZipFile(zip_file_name, 'w', zipfile.ZIP_DEFLATED) as zf:
    zf.write(file_name, arcname="docs/zipped_test_file.txt")
print(f"'{file_name}' added to '{zip_file_name}' as 'docs/zipped_test_file.txt'.")

# 2. Read from the zip archive
print(f"\nReading contents from '{zip_file_name}'...")
with zipfile.ZipFile(zip_file_name, 'r') as zf:
    print(f"Files in '{zip_file_name}': {zf.namelist()}")
    with zf.open("docs/zipped_test_file.txt") as member_file:
        read_content = member_file.read().decode('utf-8')
        print(f"Content of 'docs/zipped_test_file.txt': {read_content}")

# Clean up
os.remove(file_name)
os.remove(zip_file_name)
print("\nCleaned up dummy files.")