Introduction

When you have a large package that contains nested submodules this allows the nested submodules to refer to one another without having to pull in or know much about or explicitly import entire top-level tree. In contrast to Python's relative imports, we don't care if a file is invoked as a main program or as part of a module in the collection.

Synopsis

``` from import_relative import import_relative, get_srcdir # Below "trepan" is my top-level namespace # 'io' is the directory this file is in. Mbase = import_relative('base', '.', 'trepan') # Adds trepan.io.base # The following adds trepan.lib.bytecode Mbytecode = import_relative('bytecode', '..lib', 'trepan')

class MyClass(Mbase.InputBase): # Use name from Mbase ...

# NOTE; if your module name is "io" import like this: Mio = import_relative('trepan.io', '..') # rather than Mio = import_relative('io', '..trepan')

# like os.path.realpath(os.path.dirname(file)) srcdir = get_srcdir() srcdir = get_srcdir(1) # same as above srcdir = get_srcdir(2) # my caller's os.path.realpath(os.path.dirname(file)

```

No import path searching is done. If the imports are not there, we fail.

Rationale

In my development, each module (which is a file in Python) can be run standalone. When called as a main program, it runs demo code. Each module is responsible for importing those other modules it needs.

I have not been able to get relative imports to work. For example I get among the error messages: ValueError: Attempted relative import in non-package

or using python's -m switch: Import by filename is not supported.

Nor have I been able to use importlib either in Python 2 or 3. They seem to error out because they can't find upper-level modules or something like that.

Bugs

Sorry, we don't do "from lists".

When importing a simple name like "io" or "format" which might be around elsewhere you should add enough of the parent namespace to make the package unique.

That is instead of Mio = import_relative('io', '.') or Mio = import_relative('io', '..trepan') use: Mio = import_relative('trepan.io', '..') Here is another example I ran into. Instead of: Mformat = import_relative('format', '..lib', 'pydbgr') use: Mformat = import_relative('lib.format', '...pydbgr')

Various packing systems like pip and loaders may not work with this. This code is fragile. Down the line I'll probably redo to integrate with Python 3's importlib better.

I keep wanting to believe that there is already a way to develop out of the source code tree (not a copy of it as distutils is wont to do), not fiddle with search paths, and have demo code in modules so they can be run equally well as a main program and embedded as a module in the entire system.

Until then, I have this.

See https://code.google.com/p/pydbgr/ or https://code.google.com/p/python3-trepan/ for large projects that use this.