depends.py 文件源码

def get_module_constant(module, symbol, default=-1, paths=None):
    """Find 'module' by searching 'paths', and extract 'symbol'

    Return 'None' if 'module' does not exist on 'paths', or it does not define
    'symbol'.  If the module defines 'symbol' as a constant, return the
    constant.  Otherwise, return 'default'."""

    try:
        f, path, (suffix, mode, kind) = find_module(module, paths)
    except ImportError:
        # Module doesn't exist
        return None

    try:
        if kind == PY_COMPILED:
            f.read(8)  # skip magic & date
            code = marshal.load(f)
        elif kind == PY_FROZEN:
            code = imp.get_frozen_object(module)
        elif kind == PY_SOURCE:
            code = compile(f.read(), path, 'exec')
        else:
            # Not something we can parse; we'll have to import it.  :(
            if module not in sys.modules:
                imp.load_module(module, f, path, (suffix, mode, kind))
            return getattr(sys.modules[module], symbol, None)

    finally:
        if f:
            f.close()

    return extract_constant(code, symbol, default)