rarfile FAQ

What are the dependencies?

It depends on unrar command-line utility to do the actual decompression. Note that by default it expect it to be in PATH. If unrar launching fails, you need to fix this.

Alternatively, rarfile can use bsdtar from libarchive as decompression backend, but that is a bit problematic as bsdtar does not support all RAR features.

It depends on cryptography or PyCrypto modules to process archives with password-protected headers.

Does it parse unrar output to get archive contents?

No, rarfile parses RAR structure in Python code. Also it can read uncompressed files from archive without external utility.

Will rarfile support wrapping unrarlib/unrar.dll/unrar.so in the future?

No. The current architecture - parsing in Python and decompression with command line tools work well across all interesting operating systems (Windows/Linux/MacOS), wrapping a library does not bring any advantages.

Simple execution of command-line tools is also legally simpler situation than linking with external library.

How can I get it work on Windows?

On Windows the unrar.exe is not in PATH so simple Popen("unrar ..") does not work. It can be solved several ways:

  1. Add location of unrar.exe to PATH.
  2. Set rarfile.UNRAR_TOOL to full path of unrar.exe.
  3. Copy unrar.exe to your program directory.
  4. Copy unrar.exe to system directory that is in PATH, eg. C:\Windows.

How to avoid the need for user to manually install rarfile/unrar?

Include rarfile.py and/or unrar with your application.

Will it support creating RAR archives?

No. RARLAB is not interested in RAR becoming open format and specifically discourages writing RAR creation software.

In the meantime use either Zip (better compatibility) or 7z (better compression) format for your own archives.

What is the USE_EXTRACT_HACK?

RarFile uses unrar to extract compressed files. But when extracting single file from archive containing many entries, unrar needs to parse whole archive until it finds the right entry. This makes random-access to entries slow. To avoid that, RarFile remembers location of compressed data for each entry and on read it copies it to temporary archive containing only data for that one file, thus making unrar fast.

The logic is only activated for entries smaller than rarfile.HACK_SIZE_LIMIT (20M by default). Bigger files are accessed directly from RAR.

Note - it only works for non-solid archives. So if you care about random access to files in your archive, do not create solid archives.