rarfile FAQ¶
Table of Contents
- rarfile FAQ
- What are the dependencies?
- Does it parse
unrar
output to get archive contents? - Will rarfile support wrapping unrarlib/unrar.dll/unrar.so in the future?
- How can I get it work on Windows?
- How to avoid the need for user to manually install rarfile/unrar?
- Will it support creating RAR archives?
- What is the USE_EXTRACT_HACK?
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:
- Add location of
unrar.exe
to PATH. - Set
rarfile.UNRAR_TOOL
to full path ofunrar.exe
. - Copy
unrar.exe
to your program directory. - 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.