The following are a set of command-line-centric instructions for installing pySCA on Linux, Windows, and macOS operating systems.

1. Install Dependencies

Choose the set of instructions in this section based on your operating system.

Linux (Ubuntu 18.04)

Before installing pySCA, install the following packages from your package repository:

  1. Python 3

  2. Pip

  3. GCC

sudo apt-get install python3 python3-pip git gcc

Next, download and install FASTA from GitHub. FASTA is needed for the ggsearch36 function.

git clone
cd fasta36/src
make -j2 -f ../make/Makefile.linux all
sudo cp -r ../bin /usr/local
sudo rm /usr/local/bin/README
cd ../..

This will compile and install FASTA in the /usr/local/bin directory. This is already on your system PATH, so programs will be able to find it without additional configuration.

Alternatively, instead of ggsearch36, one can instead use the needle function from the EMBOSS software package.

macOS (10.15)

To install the dependencies on macOS, you will need to enable Xcode (xcode-select --install) and install Homebrew, and unofficial package manager.

The installation process will involve entering commands in the terminal and editing text files.

For those unfamiliar, to run commands in the terminal:

  1. Search for “terminal” in the launcher.

  2. Open the “Terminal” application.

  3. Type in a command into the terminal.

  4. Hit ENTER.

Repeat steps 3 and 4 for all the commands you need to run.

Open your terminal. Search for “terminal” in your launcher’s list of applications. The following are a set of command-line instructions.


Now, installation of dependencies. The first step is to enable macOS developer tools (i.e. Xcode). If this has not already been installed, run the following in the terminal:

xcode-select --install

You will be prompted for your password at this step.


To install Homebrew, run (copied from the Homebrew website) the following in the terminal:

/bin/bash -c "$(curl -fsSL"

You will be prompted for your password at this step.

If you run into permissions errors when installing Homebrew, complaining that root owns the /usr/local/ directory, you can change the ownership by running in the terminal:

sudo chown -R <user> /usr/local

where <user> should be substituted with your username. You can view your username in the right prompt of your open terminal windows (e.g. <user>@<host>). If still unsure, type whoami into the terminal, which will print out username name. (Don’t use sudo whoami.)

Python and GCC

Once Homebrew is installed, install Python 3 and GCC:

brew install gcc python3

This will install the most recent version of Python and the GCC compiler in your /usr/local directory. To ensure that these programs are used (rather the ones packged with the base system), add the following to your shell rc file (e.g. ~/.bashrc or ~/.zshrc, depending on what your default shell):

export CC=/usr/local/bin/gcc-9
export CXX=/usr/local/bin/g++-9
alias gcc=/usr/local/bin/gcc-9
alias g++=/usr/local/bin/g++-9

alias python=/usr/local/bin/python3
alias python3=/usr/local/bin/python3
alias pip=/usr/local/bin/pip3
alias pip3=/usr/local/bin/pip3
alias python-config=/usr/local/bin/python3-config
alias python3-config=/usr/local/bin/python3-config

If unsure of your default shell, run echo $SHELL in your terminal. If the output contains zsh, you need to edit ~/.zshrc (note the ‘.’ at the beginning of the file name), and if the output contains bash, edit ~/.bashrc.

To edit these files, you can either evoke a text editor from the terminal, or your can locate the file in your fie explorer and open it in a text editor there. If you opt to use the terminal for edits, one option is to run:

nano ~/.bashrc

(or nano ~/.zshrc as appropriate)

Go to the bottom of the file and append the block of lines above. Save the changes and exit the editor.

Next, you will need to update your shell environment to reflect the changes made by appending those lines:

  1. Option 1: Close and re-open the terminal.

  2. Option 2: Run in the terminal:

    source ~/.bashrc

Now, you can check the new aliases and environmental variables by running in the terminal:

echo $CC
echo $CXX

In the output, look for lines corresponding to the aliased commands you copied earlier, namely python and pip. Make sure they match.


Once the aliases and environmental variables are properly set, install FASTA:

git clone
cd fasta36/src
make -j2 -f ../make/Makefile.os_x86_64 all
cp -r ../bin /usr/local
rm /usr/local/bin/README
cd ../..

FASTA will now be installed in the /usr/local/bin directory, and the ggsearch36 program included in FASTA will now be on the system PATH.

If the installation fails due to permissions issues caused by root owning /usr/local/bin, you may need to use sudo to run the following:

cd fasta36/src
sudo cp -r ../bin /usr/local
sudo rm /usr/local/bin/README
cd ../..

You will be prompted for your password at this step.

Once installed, you can check that ggsearch36 is up and running by entering in the terminal:


This should print out the usage information for ggsearch36.

Windows 10

First, download and install:

  1. MSYS2,

  2. Python 3, and

  3. Git for Windows.

IMPORTANT: When opening Python 3 installer, click the checkbox to make sure Python is added to your system PATH. For the rest of the prompts, use the defaults.

Git for Windows creates both a Bash prompt with Git for version control that also can access Python 3 installation on the system PATH. Again, it’s essential that Python 3 added there. If not (or if you don’t remember), run the Python 3 installer again and make sure.

MSYS2 is a program for compiling Windows programs using a POSIX compatibility layer and ported versions of GCC, binutils, and other utilities. Essentially, one can use it to compile Windows exe’s as one would on a Unix operating system, like macOS or Linux.

The reason to install it here is to compile FASTA. Once MSYS2 is installed, open in and run:

pacman -Syu

The program will upgrade some core packages and request to be closed. Do so, re-open it, and once again run:

pacman -Syu

Once the upgrade are complete, install the following packages with the package manager (pacman) by running:

pacman -S git vim make gcc

Now, you can download and install FASTA:

git clone
cd fasta36/src
make CC=/usr/bin/gcc LD=/usr/bin/ld -j2 -f ../make/Makefile.linux all
cp -r ../bin /usr/local/
rm /usr/local/bin/README
cd ../..

Now, the ggsearch36 program, along with the others, are installed in /usr/local/bin. The next step is to add this directory into your Windows system PATH variable:

  1. Type ‘env’ in the start search bar.

  2. Click ‘Edit the system environment variables’.

  3. Click on ‘Environment Variables…’ toward the bottom of the window that opens.

  4. Select ‘Path’ in one of the two selection windows (either ‘User variables’ or ‘System variables’ is fine)

  5. Once ‘Path’ is highlighted, click ‘Edit…’

  6. Enter the /usr/local/bin as a new PATH entry. You can either:

    • Click ‘New’ in the new window and enter the path to /usr/local/bin in the MSYS2 installation folder (default: C:msys64usrlocalbin).

    • Click the ‘Browse…’ button and navigate to the C:msys64usrlocalbin directory.

  7. When the new entry is added, click ‘OK’ on all the opened windows to set all the changes. You will need to close and re-open terminals for the changes to be reflected.

Now, ggsearch36.exe will be available to all running programs.

Finally, launch Git Bash (from Git for Windows) after installed. Open the ~/.bash_profile file in the text editor, default vi, by running vi ~/.bash_profile. In this file add the lines:

alias python="winpty python.exe"
alias pip="winpty pip.exe"

Close the terminal and open it again. Now, you will be able to invoke the Python REPL and pip from the Git Bash prompt. Also, if the PATH variable was properly updated to contain the /usr/local/bin folder from the FASTA step, ggsearch36.exe will also be available in Git Bash.

You will use the Git Bash prompt to download and install pySCA.

2. Other Dependencies

The following steps are optional but highly recommended:

  1. PFAM annotations (click to download) - the file pfamseq.txt contains phylogenetic annotations for PFAM sequences. This is necessary if you would like to annotate PFAM alignments with taxonomic/phylogenetic information using the annotateMSA script provided by pySCA. The file is available from the PFAM FTP site in compressed (*.gz) format. Just be aware that the file is quite large (~10 Gb download, ~30 Gb decompressed), so check beforehand that you have available space on your hard drive.

  2. PyMol - necessary if you would like to use pySCA’s automated structure mapping scripts, and useful for mapping the sectors to structure in general.

    The version of the code provided in the linked website requires a paid license. For an open-source (free) build of the code, albeit with some functionality removed, you can follow the following instructions:

    Linux - install from your distribution package repository

    macOS - run in the terminal:

    brew cask install xquartz
    brew install brewsci/bio/pymol

    Windows - look for online builds

  3. mpld3 - a package that allows more interactive plot visualization in Jupyter notebooks. If you choose not to install this (optional) package, you will need to comment out the import mpld3 lines at the beginning of the tutorials. To install, run in the terminal:

    pip install mpld3

3. Download Code

The pySCA package, tutorials, and associated scripts are available for download from the GitHub repository. There are several options for doing so.

A. Use Git

If you have git installed on your system, you can use it to clone the repository from GitHub. From the command line, run:

git clone

For development and troubleshooting purposes, using Git is preferred.

The code will now be downloaded in a directory called pySCA.

B. (OR) Download from the Website

Though not recommended, you can also download the source code from the GitHub website. Click the green “Clone or download” tab pictured below to obtain the latest code.


In the event that you need older versions of the code, you can use the releases tab on the GitHub page to download older tagged version.

4. (OPTIONAL) Modify Settings

Before installing pySCA, for your convenience, you may specify default paths in the file found in the pysca directory of the pySCA codebase. Setting these is optional, for not doing so simply meaning having to set a few command line options when running the code later.


location of the pfamseq.txt text file (default: pfamseq.txt). Use an absolute path to specify location.


location of the pfamseq.db SQLite database (default: pfamseq.db) — the database is generated by the script and much faster to process than the text file.


location of your PDB structures for analysis (default: .). This variable should be set to the absolute path of the directory where you store all your PDB structures.


name of the directory where to output the SCA results (default: output/)


path to PyMOL executable. If unset – the default – pySCA will look for PyMOL in the system PATH. This variable will only need to be set if PyMOL is installed in an exotic location and cannot be started by simply running pymol in the terminal.

If you ever want to change these variables at a later time, edit the file and then re-install pySCA. Follow the installation procedure in the next step.

5. Install pySCA

The processing scripts found in the bin/ directory and the SCA toolbox in pysca/ can now be installed. To install them system-wide, go to the base of the repository (i.e. the pySCA/ directory downloaded by Git) and run in the terminal:

pip install .

Note the ‘.’ at the end. Don’t omit it — it tells pip to look in the current directory for configuration instructions.

Pip will first install python package dependencies:

  1. Numpy

  2. Scipy

  3. Argparse

  4. Wheel

  5. Matplotlib

Then, it install the pySCA code itself.

If and only if you run into permissions errors, two options are to either:

A. Install pySCA locally

To install pySCA in your user directory (and without root privileges), run in the terminal:

pip install --user .

This option is useful if you are working on a system where you do not have administrator access.

Note that to use locally installed scripts, the installation directory needs to be in the system PATH. To check whether that is the case, run:

echo $PATH | grep --color=auto "$(python -m site --user-base)/bin"

If the installation directory is highlighted in the output, then the PATH is configured correctly. If it is not found, then it needs to be added manually. Open you shell configuration file (e.g. ~/.bashrc) and add the directory to the PATH variable by appending the following line:

export PATH="$HOME/.local/bin:$PATH"

The exact path (the text following the semicolon) may differ on your system, but it can easily be found by running echo $(python -m site –user-base)/bin.

OR B. Install pySCA globally as root

To install pySCA system-wide, run (as root/administrator):

sudo pip install .

This will obviate any need to mess around with local PATH variables, and pySCA will be accessible to all users on the system.

Now, with the pySCA code installed, each of the commands found in bin/ can now be run from the command line.

6. Getting Started and Running the Tutorials

The “getting started” section of this documentation provides instructions on how to run some initial calculations and the tutorials. The basic idea behind the pySCA code is that the core calculations are performed using a series of executable Python scripts, and then the results can be loaded and analyzed/visualized using an Jupyter notebook (or alternatively, MATLAB).

All of the tutorials are written provided as Jupyter notebooks. For more on how Jupyter notebooks work, see: Prior to running the notebook tutorials, you’ll need to run the core calculation scripts that generate the input for the notebooks. One way to do this is with the shell script “”, and there is more information on this in the “getting started” section. Once the calculations are completed, you can begin the tutorial in interactive Python from the command line, by typing:

To install Jupyter, run:

pip install jupyterlab

You can then open the notebooks from the command line by running:

jupyter notebook <notebook.ipynb>