How to Access Parent/Sibling Module Methods

How to access parent/sibling module methods

Constants are looked up first in the lexically enclosing module(s) and then up the inheritance chain.

module Foo
  module Bar
    module Baz
      class Qux
        def self.qux_method
          Baz.baz_method    
        end
      end
      def self.baz_method
      end
    end
  end
end

This will work, because the constant Baz will be first looked up in the lexically enclosing module (class) Qux, where it isn't found. The lookup continues in the lexically enclosing module Baz, where it also isn't found. Therefore, it will next be looked up in the lexically enclosing module Bar, where it is found and the search stops.

Note: you write in your title:

Ruby, Access parent/sibling module methods

This is wrong. These modules are neither parents nor siblings. There is no inheritance here. There is, in fact, no relationship between the modules at all. There is only a relationship between the constants and the modules: constants belong to modules.

The module declarations are lexically nested, but the modules themselves aren't.

Ruby: get a sibling module

It's simpler than you thought

module ParentModule
  module Foo
    def self.get_bar
      Bar
    end
  end
end

The :: you tried with, it instructs ruby to look this name up in the top-level scope. If you omit it, ruby will first look in the current scope, then its parent, then its parent, and all the way to the top-level.

So, ParentModule::Foo::Bar will not be found, but ParentModule::Bar will be.

Sibling package imports

Seven years after

Since I wrote the answer below, modifying sys.path is still a quick-and-dirty trick that works well for private scripts, but there has been several improvements

• Installing the package (in a virtualenv or not) will give you what you want, though I would suggest using pip to do it rather than using setuptools directly (and using setup.cfg to store the metadata)
• Using the -m flag and running as a package works too (but will turn out a bit awkward if you want to convert your working directory into an installable package).
• For the tests, specifically, pytest is able to find the api package in this situation and takes care of the sys.path hacks for you

So it really depends on what you want to do. In your case, though, since it seems that your goal is to make a proper package at some point, installing through pip -e is probably your best bet, even if it is not perfect yet.

Old answer

As already stated elsewhere, the awful truth is that you have to do ugly hacks to allow imports from siblings modules or parents package from a __main__ module. The issue is detailed in PEP 366. PEP 3122 attempted to handle imports in a more rational way but Guido has rejected it one the account of

The only use case seems to be running scripts that happen
to be living inside a module's directory, which I've always seen as an
antipattern.

(here)

Though, I use this pattern on a regular basis with

# Ugly hack to allow absolute import from the root folder
# whatever its name is. Please forgive the heresy.
if __name__ == "__main__" and __package__ is None:
    from sys import path
    from os.path import dirname as dir

    path.append(dir(path[0]))
    __package__ = "examples"

import api

Here path[0] is your running script's parent folder and dir(path[0]) your top level folder.

I have still not been able to use relative imports with this, though, but it does allow absolute imports from the top level (in your example api's parent folder).

Import from sibling directory

You really should be using packages. Then MainDir is placed at a point in the file system on sys.path (e.g. .../site-packages), then you can say in ClassB:

from MainDir.Dir.DirA import ClassA # which is actually a module

You just have to place files named __init__.py in each directory to make it a package hierarchy.

How to import a Python module from a sibling folder?

This is happening because A and B are independent, unrelated, packages as far as Python is concerned.

Create a __init__.py in the same directory as Driver.py and everything should work as expected.

How to import python modules from sibling directory?

Since there are already many answers on SO for this*, I will focus on question (2). About what is a better code organization:

|- setup.py
|- top_pkg_name
    |- __init__.py
    |- pkg1
        |- __init__.py
    |- pkg2
        |- __init__.py

The (relative) import is done as follows, from inside module_2:

from ..pkg1 import module1 as m1

Alternatively, you can use absolute imports, which refer to the top package name:

from top_pkg_name.pkg1 import module1 as m1

In such an organization, when you want to run any module as a script, you have to use the -m flag:

python -m top_pkg_name.pkg1.module1

For question (3), I'm not sure but it looks like the unittest module adds the folder to path, allowing the imports to happen directly.

*Refer:

1. How do I import a Python script from a sibling directory?
2. Python import module from sibling folder

Xpath expression to access parent or sibling using HTML::TreeBuilder::XPath module

The error message is misleading. The problem isn't lack of support, it's that you're trying to find the parent of the boolean returned by the comparison. It doesn't have one.

You could use

//*[ td[@class="c1" and text()="Match_Text"] ]/td[@class="c2"]

//td[@class="c1" and text()="Match_Text"]/following-sibling::*

//td[@class="c1" and text()="Match_Text"]/following-sibling::td[@class="c2"]

//td[@class="c1" and text()="Match_Text"]/../td[@class="c2"]

---

Related Topics