# This instruction is for Unix-like OS users.
# I refered to the following guide when I wrote it.
# https://conda.io/docs/user-guide/tasks/build-packages/recipe.html

# Activate an environment if needed
conda activate myenv

# Install conda-build if you haven't. Ironically, installing conda-build
# includes installing python. This python will be effectively replaced with
# your new python binary so don't worry.
conda install conda-build

# Make a directory. You can give it any name.
mkdir python-dbg
cd python-dbg

# Download example files(meta.yaml, build.sh) from
# https://github.com/conda/conda-recipes
wget https://raw.githubusercontent.com/conda/conda-recipes/master/python/python-3.5/meta.yaml
wget https://raw.githubusercontent.com/conda/conda-recipes/master/python/python-3.5/build.sh

# Modify the downloaded files. You change them to build a different version of
# Python or to add compile flags. Refer to Python developer's guide to learn
# more about build options. https://devguide.python.org/setup/

# For example, you can make following changes in build.sh
#
# ./configure --enable-shared --enable-ipv6 --prefix=$PREFIX --with-pydebug
# make -j16

cd ..
# Hope that the build will succeed or you have to figure out
# how to solve the build problem on your own.
conda-build python-dbg

# When conda build is finished, read the log message carefully and find
# the package filename and location. In my case, it looked as below
#    ..../conda-bld/linux-64/python-3.5.0b4-0.tar.bz2
# This is what's called a package in conda

# Actually install the package
# This part is not documented well in the official conda tutorial so I
# figured it out by reading `conda install -h` message. I'm not sure if
# this is the official way to install, but it worked for me.
conda install --use-local ..../conda-bld/linux-64/python-3.5.0b4-0.tar.bz2

# Make sure if python has been installed
conda list | grep python

# Make sure a python-with-pydebug(ex. python3.5dm) was installed along with
# a normal python(ex. python3.5m) 
which python3.5
which python3.5dm