[Scons-users] Importing Module That is a Build Product

[William Blevins]

Keith,

I don't think this is related to module search path. Let me make sure I
understand.

1. Build A creates A.py.
2. Build B takes source A.py and creates B.txt.
3. SConstruct/SConscript containing Builder B imports A.py.

This will always fail on the first iteration. SConstruct/SConscripts are
always parsed in full prior to any build step. A.py will never exist prior
to the import.

V/R,
William

On Thu, Sep 15, 2016 at 1:32 PM, Keith F Prussing <kprussing74 at gmail.com>
wrote:

> Hello,
>
> I am trying to understand the behavior of SCons when trying to import a
> module in one build rule that is the product of another build rule.
> Consider the following example SConstruct:
>
>    def writeit(target, source, env):
>        """Generate a mfe module."""
>        with open(str(target[0]), "w") as fid:
>            fid.write("string = 'hello'\nconst = 1\n")
>
>        return
>
>    def useit(target, source, env):
>        """Use the mfe module."""
>        # import imp, os
>        # path, base = os.path.split(os.path.realpath(str(source[0])))
>        # name, _ = os.path.splitext(base)
>        # file, pathname, description = imp.find_module(name, [path])
>        # imp.load_module(name, file, pathname, description)
>
>        import mfe
>        with open(str(target[0]), "w") as fid:
>            fid.write("{0}\n{1}\n".format(mfe.string, mfe.const+1))
>
>        return
>
>    test1 = Builder(action=writeit)
>    test2 = Builder(action=useit)
>
>    env = Environment(BUILDERS={"writeit" : test1, "useit" : test2})
>    mod = env.writeit(target=["mfe.py"], source=[])
>    out = env.useit(target=["test.txt"], source=mod)
>
> If I run this as is, the build for 'test.txt' will fail with an
> ImportError claiming that it cannot find 'mfe' even if I build 'mfe.py'
> explicitly before building 'test.txt'.  On the other hand, if there is a
> module in the current SConstruct directory, SCons will happily import that
> module with no problems.  My end goal is to generate a module of constants
> to use in the Python parts of my build from a source in a different
> language so that all pieces are using the same values.
>
> I suspected that the problem revolved around the module search path, so
> I played around and came up with the commented work around (lines
> 10-14).  With these lines uncommented, the build for 'test.txt' proceeds
> as expected.
>
> So, my question is: How does SCons establish the module search path?  Is
> there a better way to actually get the generated module imported?
>
> Searching for variations on 'scons import error' and 'scons import
> ignoring current directory' primarily turned up hits revolving around
> importing SCons components or where to put custom builders and tools.
>
> Keith
>
> --
> Keith F Prussing
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>
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