228 lines
7.8 KiB
Plaintext
228 lines
7.8 KiB
Plaintext
PEP: 262
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Title: A Database of Installed Python Packages
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Version: $Revision$
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Author: A.M. Kuchling <akuchlin@mems-exchange.org>
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Type: Standards Track
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Created: 08-Jul-2001
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Status: Draft
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Post-History: 27-Mar-2002
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Introduction
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This PEP describes a format for a database of Python packages
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installed on a system.
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Requirements
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We need a way to figure out what packages, and what versions of
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those packages, are installed on a system. We want to provide
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features similar to CPAN, APT, or RPM. Required use cases that
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should be supported are:
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* Is package X on a system?
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* What version of package X is installed?
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* Where can the new version of package X be found? (This can
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be defined as either "a home page where the user can go and
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find a download link", or "a place where a program can find
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the newest version?" Both should probably be supported.)
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* What files did package X put on my system?
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* What package did the file x/y/z.py come from?
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* Has anyone modified x/y/z.py locally?
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Database Location
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The database lives in a bunch of files under
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<prefix>/lib/python<version>/install/. This location will be
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called INSTALLDB through the remainder of this PEP.
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The structure of the database is deliberately kept simple; each
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file in this directory or its subdirectories (if any) describes a
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single package.
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The rationale for scanning subdirectories is that we can move to a
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directory-based indexing scheme if the package directory contains
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too many entries. For example, this would let us transparently
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switch from INSTALLDB/Numeric to INSTALLDB/N/Nu/Numeric or some
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similar hashing scheme.
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Database Contents
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Each file in INSTALLDB or its subdirectories describes a single
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package, and has the following contents:
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An initial line listing the sections in this file, separated
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by whitespace. Currently this will always be 'PKG-INFO
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FILES'. This is for future-proofing; if we add a new section,
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for example to list documentation files, then we'd add a DOCS
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section and list it in the contents. Sections are always
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separated by blank lines.
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PKG-INFO section
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An initial set of RFC-822 headers containing the package
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information for a file, as described in PEP 241, "Metadata for
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Python Software Packages".
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A blank line indicating the end of the PKG-INFO section.
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FILES section
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An entry for each file installed by the package. Generated files
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such as .pyc and .pyo files are on this list as well as the original
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.py files installed by a package; their checksums won't be stored or
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checked, though.
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Each file's entry is a single tab-delimited line that contains
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the following fields:
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* The file's full path, as installed on the system.
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* The file's size
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* The file's permissions. On Windows, this field will always be
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'unknown'
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* The owner and group of the file, separated by a tab.
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On Windows, these fields will both be 'unknown'.
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* An MD5 digest of the file, encoded in hex.
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A package that uses the Distutils for installation should
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automatically update the database. Packages that roll their own
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installation will have to use the database's API to to manually
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add or update their own entry. System package managers such as
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RPM or pkgadd can just create the new 'package name' file in the
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INSTALLDB directory.
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API Description
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There's a single fundamental class, InstallationDatabase. The
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code for it lives in distutils/install_db.py. (XXX any
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suggestions for alternate locations in the standard library, or an
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alternate module name?)
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The InstallationDatabase returns instances of Package that contain
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all the information about an installed package.
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XXX Several of the fields in Package are duplicates of ones in
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distutils.dist.Distribution. Probably they should be factored out
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into the Package class proposed here, but can this be done in a
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backward-compatible way?
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InstallationDatabase has the following interface:
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class InstallationDatabase:
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def __init__ (self, path=None):
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"""InstallationDatabase(path:string)
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Read the installation database rooted at the specified path.
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If path is None, INSTALLDB is used as the default.
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"""
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def get_package (self, package_name):
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"""get_package(package_name:string) : Package
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Get the object corresponding to a single package.
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"""
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def list_packages (self):
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"""list_packages() : [Package]
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Return a list of all packages installed on the system,
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enumerated in no particular order.
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"""
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class Package:
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"""Instance attributes:
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name : string
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Package name
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files : {string : (size:int, perms:int, owner:string, group:string,
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digest:string)}
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Dictionary mapping the path of a file installed by this package
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to information about the file.
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The following fields all come from PEP 241.
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version : distutils.version.Version
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Version of this package
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platform : [string]
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summary : string
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description : string
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keywords : string
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home_page : string
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author : string
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author_email : string
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license : string
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"""
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def add_file (self, path):
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"""add_file(path:string):None
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Record the size, ownership, &c., information for an installed file.
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XXX as written, this would stat() the file. Should the size/perms/
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checksum all be provided as parameters to this method instead?
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"""
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Deliverables
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A description of the database API, to be added to this PEP.
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Patches to the Distutils that 1) implement an InstallationDatabase
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class, 2) Update the database when a new package is installed. 3)
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add a simple package management tool, features to be added to this
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PEP. (Or should that be a separate PEP?) See [2] for the current
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patch.
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Rejected Suggestions
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Instead of using one text file per package, one large text file or
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an anydbm file could be used. This has been rejected for a few
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reasons. First, performance is probably not an extremely pressing
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concern as the package database is only used when installing or
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removing packages, a relatively infrequent task. Scalability also
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likely isn't a problem, as people may have hundreds of Python
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packages installed, but thousands seems unlikely. Finally,
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individual text files are compatible with installers such as RPM
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or DPKG because a package can just drop the new database file into
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the database directory. If one large text file or a binary file
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were used, the Python database would then have to be updated by
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running a postinstall script.
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On Windows, the permissions and owner/group of a file aren't
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stored. Windows does in fact support ownership and access
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permissions, but reading and setting them requires the win32all
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extensions, and they aren't present in the basic Python installer
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for Windows.
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References
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[1] Michael Muller's patch (posted to the Distutils-SIG around 28
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Dec 1999) generates a list of installed files.
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[2] A patch to implement this PEP will be tracked as
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patch #562100 on SourceForge.
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http://www.python.org/sf/562100
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Acknowledgements
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Ideas for this PEP originally came from postings by Greg Ward,
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Fred L. Drake Jr., Thomas Heller, Mats Wichmann, and others.
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Many changes and rewrites to this document were suggested by the
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readers of the Distutils SIG.
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Copyright
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This document has been placed in the public domain.
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Local Variables:
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mode: indented-text
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indent-tabs-mode: nil
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End:
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