Some Improvements of the Python Language

Recently I have been reading a lot of Python code and noticed several improvements of the language that are really useful and wished that I had knew earlier since some of the changes were added to the Python language specification back from Python 3.5.

One improvement is the Type Hints (PEP 484, implemented in Python 3.5). It allows developers to add a type after a function parameter and a return type, which allows the code reader or another developer to understand what types are intended for the parameters. There is no checking of the actual parameter types being passed. The following example from the PEP 484 page explains its usage.

def greeting(name: str) -> str:
    return 'Hello ' + name

Another nice improvement is the new string formatting method introduced in Python 3.6 under “Formatted string literals.” It allows one to add Python variable values (or even calls) to a string object. Previously one has to use the “.format()” method to format a string. The example below explains how convenient it is now with the method.

def greeting(name: str) -> str:
    return f'Hello {name}'
emacs Linux

Configuration for Developing R code with ESS

It has been close to 10 years since I use R seriously last time. Back then I used ESS in Emacs to do all the editing and interactive sessions. I really liked it back then and I would like to check it out how ESS has evolved through the years. A quick glimpse of the ESS manual suggests it has got a lot of improvements and the Bioconductor project has evolved as well. For example, even the package installation package has changed in Bioconductor.

Unfortunately, I have forgotten the tricks and configurations that I have used to set up my ESS and Emacs environment. Below are a few things that I had to go through.

$sudo apt install -y r-cran-devtools
$sudo apt install libcurl4-gnutls-dev

The above two packages are required for quite some other R packages. To make sure the user library path is loaded correctly, I had to set the following environmental variable:

export R_LIBS="~/.local/R/lib"

The above setting works for starting R in Terminal. To make the local R library (in my home directory with no root privileges required) work with the ESS R session, I had to create a ~/.Rprofile file with the following content:


Now my Emacs speaks ESS well. I can install packages to my local libraries by default and use Emacs to edit R code in one frame and run an interactive R session in another frame and use “C-c C-c” to execute a selected region in the R code frame.

emacs Linux

Setup NCBI E-utilities

The E-utilities toolbox from NCBI is the recommended way to access NCBI and NLM data, including the genome data. The following command can easily install it in the Ubuntu Linux distribution.

$sudo apt update
$sudo apt install ncbi-entrez-direct

After successful installation you can test it out using the following example code, which provides ftp path to the first 10 Bacillus cereus in refseq. Unfortunately, this code needs to run in the BASH shell. Running it in eshell (within Emacs) does not work.

$esearch -db assembly -query "Bacillus cereus " | efetch -format docsum -mode json|grep "ftppath_refseq" |head -10
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",
            "ftppath_refseq": "",


View PDF in Emacs

Be default PDF files are opened by Docviewer in Ubuntu distributes. Yet, there is a more convenient PDF tool, aptly named pdf-tools that works well with Emacs. The installation of pdf-tools is straight forward. Below is what I did.

sudo apt install libpng-dev zlib1g-dev
sudo apt install libpoppler-glib-dev
sudo apt install libpoppler-private-dev

After that, go to Emacs and use the package-install to install

package-install pdf-tools

Finally, add the following line to the .emacs file. And make sure that if you are displaying line numbers in emacs, make sure it is disabled in pdf-view-mode. Here what I used is to just enable line number display in prog-mode.

(add-hook 'prog-mode-hook 'linum-on)


Switch Frame Quickly in Emacs

Switching between multiple frames in Emacs is a pain when you have more than two frames open. I just noticed that the ace-window package offers the function for fast frame switching. All you need to do is to put the following configuration to the .emacs file and use the “M-o” key combination then pickup the frame number in red, and you will switch to that frame.

(global-set-key (kbd "M-o") 'ace-window)

Open Virtual Box File through SSH with Emacs

The Emacs Dire mode works for remote files through SSH and FTP. Detailed documentation about how to open remote files from Emacs can be found here. With a proper setting, one can use Emacs to work directly to open files in Virtual Box without having to set the target directory as a shared resource between the host and client. In a previous post, I showed how to add the private key used by Vagrant to access Virtual Box and find out the port number for SSH connection, in this post, you will see how it will benefit you as an Emacs user.


Once you are in Emacs, use the command “Ctrl x + Ctrl f” to open file just like you would with a local file, then you use the command above to open the remote directory “/vagrant” in a Emacs frame. Of course, this command requires that you have already added the private key to your host SSH key settings and 2222 is the correct port number.


Update Kernel in Ubuntu

The Linux kernel (v5.4.0) used in Ubuntu 20.04 has poor support for the HDMI sound support—the sound device shows “Dummy Output” after every computer sleep. I had tried different solutions but still would like to forget about running those commands before getting the sound out. So, I upgraded the kernel to the latest version supported by Ubuntu and it works. Below is the list of commands that I used.

$ wget
$ sudo install /usr/local/bin/
$ sudo -i
Finding latest version available on
Latest version is: v5.7.0, continue? (y/N)
$ sudo update-grub
$ sudo grub-customizer

Since I used grub-customizer to manage Grub options, I also ran the last two commands to add the new kernel to boot options in Grub. After reboot the computer with the new kernel, I no longer have the “Dummy Output” issue any more.


Copy files from a Virtual Box managed by Vagrant

Vagrant is a very useful tool for setting up a development environment. With vagrant, you can manage Virtual Box easily. However, if you have not set up the shared directory correctly, getting access to the file in the virutal box from the local host is tricky. Below is a solution using the scp command.

vagrant ssh-config

Which gives you the identity key used by vagrant as well as the port number of the virtual box.

  User vagrant
  Port 2222
  UserKnownHostsFile /dev/null
  StrictHostKeyChecking no
  PasswordAuthentication no
  IdentityFile /yourhome/.vagrant/machines/default/virtualbox/private_key
  IdentitiesOnly yes
  LogLevel FATAL

That’s all you need to put into the scp command:

scp -i /yourhome/.vagrant/machines/default/virtualbox/private_key -p 2222 -r vagrant@ local_dir

Notice here after “-i” is the key file reported by “vagrant ssh-config” command. Similarly the port number 2222 also came from there.

To avoid type “-i” option in the future, one can use the command below to permanently add the private key to SSH configuration so that only the port number is used in the future.

ssh-add /yourhome/.vagrant/machines/default/virtualbox/private_key


Emacs File Explorer Solution

I just came across the Treemacs package that I wish I knew earlier. Treemacs is an Emacs package that provides a tree layout file explorer for Emacs. With Treemacs, one can easily navigate through a big project tree all in Emacs.

Installation is simple through ELPA. I have the following lines in my .emacs configuration:

(setq package-archives '(("gnu" . "") ))
(when (>= emacs-major-version 24)
  (require 'package)
  (add-to-list 'package-archives '("melpa" . "") t)    

In Emacs, run “M-x package-refresh-contents”, then “package-install treemacs.” After installation, run “M-x treemacs” brings up the tree view.


Ubuntu Dummy Output Audio Solution

Recently I upgraded to Ubuntu 20.04, after which I experienced the problem of “dummy output” audio. After leaving the computer to sleep, Ubuntu will set the sound to Dummy Output. A reboot or log out and then login in again always solve the problem. Some quick Internet searches suggest this is a common problem and may be related to the new kernel ( 5.4.0) in Ubuntu 20.04. I have tried solutions that I found on-line but they didn’t solve the problem, including the command “pulseaudio -k,” which was reportedly solved the problem in some cases.

However, running the command “pulseaudio –start” after “pulseaudio -k” solved my problem.