Well, things have been a little quiet on this list. Time to shake it up a bit, methinks. So I've written a design proposal -- here it is. (NB. #1: to avoid sounding overly wafflish, I've written this in a fairly imperious way -- "X will be done this way, Y is like that". Don't take it *too* seriously; this is open for discussion, up for grabs, welcomes your comments and criticisms, etc. Of course, I wouldn't have designed it this way if I didn't think it was good idea, so expect a reaction if you tell me I'm full of baloney... ;-) (NB. #2: this file is in the Distutils CVS archive as 'text/design-proposal.txt'. Once it is better firmed up through the discussion that I'm sure is forthcoming, I'll HTMLify it, put it in the SIG's web space, and start coding!) $Id: design-proposal.txt,v 1.1 1999/01/11 04:06:01 gward Exp $ RECAP: User Interface ===================== Recall from the proposed user interface (posted at http://www.python.org/sigs/distutils-sig/interface.html) that the Distutils will operate via a (usually) trivial Python script, conventionally called setup.py. setup.py has the following syntax: setup.py [global_options] cmd [cmd_options] (XXX no provision for multiple commands here! shouldn't be hard, though, as long as we're firm about what a command is and what an option is) The Distutils will define a standard set of global command-line options; each Distutils command will define a set of command options. The module developer (the person who wrote the setup.py for his module distribution) may define a set of distribution-specific command-line options, which will be mixed in with the global options (and extracted from them before they can cause any harm). The first order of business to decide on the set of standard Distutils commands. Again, from the proposed interface, here is my initial list: make_blib - create mockup installation tree ("build library") build_py - copy/compile .py files (pure Python modules) build_ext - compile .c files, link to .so in blib build_doc - process documentation (targets: html, info, man, ...?) build - build_py, build_ext, build_doc dist - create source distribution bdist - create built distribution for current platform test - run test suite install - install on local machine please see the above URL for details on these. REAL STUFF: Proposed Design =========================== Part 1: from the Distutils' point of view ----------------------------------------- setup.py only has to import one module, 'distutils.core'. This module is responsible for parsing all command-line arguments to setup.py (even though the interpretation of options is distributed across the various Distutils commands, and possibly the client setup.py). It also takes care of receiving control from setup.py, and passing it as appropriate to Distutils commands. Most importantly, 'distutils.core' defines the 'Distribution' class, which is the heart and soul of the Distutils. The client (setup.py) exists mainly to provide attributes for a 'Distribution' instance, and all the Distutils commands operate on that instance. Speaking of Distutils commands: each one is implemented as a Python module, e.g. the 'build' command is implemented by the 'distutils.build' module. Each command module is required to define one function, also named for the command -- e.g. 'distutils.build.build'. This function takes a 'Distribution' instance as its only required argument, and then "does its thing" (eg. build extensions, install everything, etc.). All information needed to "do its thing" is contained in the 'Distribution' instance. (XXX this isn't very OO. As long as we can fully parameterize Distutils commands, that's fine: the client (or user) just provides attributes to go into a 'Distribution' instance, and the command modules use those attributes to know what to do. Inevitably, though, someone somewhere will have to override actual code, and this scheme will break down -- either that or we'll have to put a lot of command-specific stuff into the 'Distribution' class, which is bad [makes it harder to add new commands]. A possible alternate formulation: have each command module define a specially-named class, which is then used to "do its thing". If a client setup.py needs to override, say, installation behaviour, then it can create a subclass of distutils.install.Install. It would then need to tell the 'Distribution' class to use its derived class -- not an impossible task!) Part 2: from the client's point of view --------------------------------------- As I said above, the client (setup.py) only has to import 'distutils.core' -- everything else Distutils-ish is taken care of by this core module. However, the client needs a way to communicate its particular options into the Distutils core (and out to the command modules). I have two possible schemes for this: one short and convenient (but not too extensible), and the other a bit verbose and clunky (but more OO and extensible). There's no reason we can't have our cake and eat it too; the convenient interface could just be a wrapper for the full-blown interface for the many module distributions that don't need a lot of fancy customization. First, here's an example of the simple interface, used for a module distribution with a single "pure Python" module (mymod.py). ------------------------------------------------------------------------ from distutils.core import setup setup (name = "mymod", version = "1.2", author = "Greg Ward <gward@cnri.reston.va.us>", description = "A very simple, one-module distribution") ------------------------------------------------------------------------ Note that we don't explicitly list "mymod.py" anywhere: Distutils assumes that this is a one-horse distribution named after its sole module ('mymod'). Those who enjoy defining subclasses might prefer to phrase this differently: ------------------------------------------------------------------------ from distutils.core import Distribution, setup class MyDistribution (Distribution): name = "mymod" version = "1.2", author = "Greg Ward <gward@cnri.reston.va.us>", description = "A very simple, one-module distribution") setup (distclass = MyDistribution) ------------------------------------------------------------------------ This is overkill for a small distribution: we're defining a new class solely to provide attribute values, when the 'distutils.core.setup' exists mainly to let do this anyways. Nevertheless, OO purists will like this -- and undoubtedly there will be times when the client *will* have to override behaviour -- not just data -- and the OO interface will be necessary. And more complex module distributions, with lots of attributes to customize, might be easier to read/maintain with things broken up like this. Consider a distribution with two pure Python modules ('mymod' and 'my_othermod') and a C extension ('myext'); the C extension must be linked with two ancillary C files and a C library. Oh yeah, this distribution requires Python 1.5 and any version of the 're' module: ------------------------------------------------------------------------ from distutils.core import Distribution, setup class MyDistribution (Distribution): name = "mydist", version = "1.3.4", author = "Greg Ward <gward@cnri.reston.va.us>" description = """This is an example module distribution. It provides no useful code, but is an interesting example of the Distutils in action.""" # Dependencies requires = { 'python': '1.5', # I like class-based exceptions 're': '', # and I love Perl-style regexps! ;-) } # (and yes, I *know* that "Python 1.5" # implies 're'...) # Actual files that need to be processed and installed in some form py_modules = ['mymod.py', 'my_othermod.py'], ext_modules = {'myext.c': {'other_c': ['extra1.c', 'extra2.c'], 'c_libraries': ['mylib']} } setup (distclass = MyDistribution) ------------------------------------------------------------------------ A couple of things to note: * I'm not afraid to use deeply nested data structures; if you're writing and distributing Python modules, this shouldn't be a problem! * every attribute has a particular type (string, list, dictionary, ...) * the attributes with complex types (especially dictionaries) will have a well-known and well-documented internal structure: eg. """ext_modules is a hash mapping names of C source files (each containing a Python extension module) to a nested hash of information about how to build that module. The allowed keys to this nested hash are: - other_c: other C files that must be compiled and linked with the main C file to create the module - c_libraries: C libraries that must be included in the link ... """ No doubt the 'ext_modules' nested hashes would have more options, and no doubt other Distribution attributes would have complex, documented structure. Finally, the list of all Distribution attributes must be well-known and well-documented! These seem to fall into a couple of broad categories. Here's an initial attempt at a list: Distribution meta-data name version author description Dependencies requires Files to be processed and installed py_modules ext_modules doc_files [eg. SGML source - or whatever std. we get for documentation] Build directories [all under "./blib" by default] build_lib - where to put platform-independent library files build_platlib - where to put platform-dependent library files build_exe - where to put executable programs (ie. scripts) build_html - where to put processed documentation (HTML) (etc... more documentation formats, at least) Installation directories [under sysconfig.LIBDEST] install_lib install_platlib install_exe install_html C compilation cc ccshared cflags ldflags ...well, that's a start. I still don't know how to make all those Unixish C compilation variables more cross-platform. Part 3: revisiting the Distutils' point of view ----------------------------------------------- To sum up, let's go through what happens when the user runs 'setup.py'. Whether setup.py is written in the simple (call-a-function) or general (define-a-subclass) form doesn't matter too much, so I won't split things up into two streams. * setup.py imports distutils.core * distutils.core startup code parses command-line arguments: processes global options that it knows about, and saves the rest for the client (setup.py) to deal with; saves the command, and saves the command-specific options for passing to the command module * setup.py calls distutils.core.setup (possibly with a 'distclass' argument specifying a subclass of Distribution) * distutils.core.setup instantiates Distribution (or the subclass supplied by the client), and uses its arguments (apart from 'distclass') to override attributes of this instance * distutils.core.setup loads the command module (eg. 'distutils.build') * distutils.core.setup calls the command module's interface function (eg. 'distutils.build.build'), passing it the Distribution instance and any command-specific options from the setup.py command-line * [alternate formulation: distutils.core.setup instantiates the command module's interface class (eg. 'distutils.build.Build', or an alternate supplied by the client using the as-yet-unmentioned 'command_class' attribute. The Distribution instance and all command-specific options are supplied to the command class so it can "do its thing"] (XXX again, no provision for multiple commands, although it shouldn't be too hard. And the OO approach to writing command modules needs to be better fleshed out.) Part 4: Unresolved issues ------------------------- * Where do we take care of platform dependencies? Somewhere, sometime, we'll need a class or function or attribute named 'foo_posix', 'foo_win32', 'foo_mac', etc. We might also need 'foo_linux_i86', 'foo_solaris2, 'foo_irix5', 'foo_winnt', 'foo_win98', 'foo_macos8', etc. * ...And that's just within Distutils itself. What about client code -- what if I have a module that sets itself up differently for different distributions; how do I specify that? * Recusive setup: what if my distribution has subdirectories containing other module distributions, with their own setup.py's? Will this ever be needed. (Undoubtedly.) How does the client specify them, and how does the Distutils run them? -- Greg Ward - software developer gward@cnri.reston.va.us Corporation for National Research Initiatives 1895 Preston White Drive voice: +1-703-620-8990 x287 Reston, Virginia, USA 20191-5434 fax: +1-703-620-0913