divmod-dev team mailing list archive

[Zooko O'Whielacronx <zooko@xxxxxxxxx>]

Ivan Kozik asked me on Stack Overflow to explain why it could matter,
for Python packages in general, whether they import themselves when
building. I managed to explain the ways that it can be a problem better
this time around than before:

http://stackoverflow.com/questions/458550/standard-way-to-embed-version-
into-python-package/7071358#7071358

Below I'll copy and edit what I wrote there:

If your setup.py is being executed in a freshly created Python process,
and your current working directory is the directory that contains the
version of your project that it is building, and any dependencies that
your project imports when it is imported are already installed, then it
will work.

This is the common way that programmers run setup.py, so they often
think it is the only way. But there are other ways that setup.py gets
evaluated! Tools like py2exe run a single Python process and then load
and execute the setup.py scripts from one project after another (while
packing them all together). Suppose that some of the Python code that
ran before your setup.py script imported a different version of your
module. In that case, "import yourniftymodule" in your setup.py would
find that *different* version in your sys.modules. (This has happened to
me with Nevow.)

Another problem is if the user is using a tool like setuptools or pip to
install your package. Such a tool needs to do two things for packages
that declare dependencies: 1. build this package, 2. install (first
building, if necessary) its dependencies. Now, what order should the
tool do this in?

It can't (in the setuptools/pip/virtualenv system of today) even know
what the deps are until it evaluates your setup.py. Also, if it tried to
do full depth-first and finish installing all deps before it builds this
package, it would get stuck if there were circular deps. But if it tries
to build this package before installing the dependencies, then if you
import your package from your setup.py, it will not necessarily be able
to import its deps, or the right versions of its deps.

-- 
You received this bug notification because you are a member of Divmod-
dev, which is the registrant for nevow.
https://bugs.launchpad.net/bugs/812537

Title:
  build Nevow without importing Nevow

Status in Divmod Nevow:
  New

Bug description:
  This looks like a good patch:

  http://bazaar.launchpad.net/~divmod-dev/divmod.org/build-nevow-
  without-importing-2699/revision/2601

  But why do the execfile hack only when setuptools is present? Why not
  do that same thing in both cases?

To manage notifications about this bug go to:
https://bugs.launchpad.net/nevow/+bug/812537/+subscriptions