python “ModuleNotFoundError: No module named '_ctypes'” error on a shared host (no ability to sudo install libffi-dev)

Question

I'm on a shared host, and they're running CentOS with an ancient version of python that lacks pretty much everything. I've compiled python 3.8, and that works, but when I try to run anything with pip or running a setup.py file, I keep getting the

ModuleNotFoundError: No module named '_ctypes'

error.

How do I get _ctypes support into a Python I build if I don't have root access?

Assorted things I've already tried:

1. Looking for a portable version of python - but I could only find windows portable versions.
2. Found a ctypes extension to install to python - couldn't even try because it ran by a setup.py which still wants ctypes (my guess is some kind of extension to existing ctypes?)
3. Yum - I have no access.
4. Contacting my hosting provider... they won't install it for me, say I have to build it myself if I want it even though the library I need (libffi-dev) requires sudo access that I don't have to build it.

Answer 1

I have been scratching my head for the past 3 days and nothing seemed to work. However, setting some flags helped. I assume you want to build without root access in CentOS. One key point is using --with-system-ffi flag. Details below and good luck.

Step-1: ensure libffi is installed Step-2: assign Path Step-3: install Python with proper flags

downloaddir='where you download zipped pacakges'
packagedir='where you unpack/unzip your downloaed files'
installdir='where you make local install'
threads=2 # number of threads available to accelerate installation

Install libffi

libffi_version=3.3
cd ${downloaddir}
wget ftp://sourceware.org/pub/libffi/libffi-${libffi_version}.tar.gz
tar xfvz libffi-${libffi_version}.tar.gz -C ${packagedir}
cd ${packagedir}/libffi-${libffi_version}/
./configure -v --prefix=${installdir} --disable-static
make -j${threads}
make install

For your whole set of GEOPACKAGES, you will need to assign the following system variables (not just for libffi but all packages):

export PATH=...
export CPATH=...
export LD_LIBRARY_PATH=...
export LIBRARY_PATH=...
export PKG_CONFIG_PATH=...<pkconfig>
export DSQLITE3_INCLUDE_DIR=...<sqlite3 header>
export DSQLITE3_LIBRARY=...<sqlite3 lib>
export LD_RUN_PATH=...<libdir>

Install Python in CentOS without root access

python_version=3.8.0
    cd ${downloaddir}
    wget https://www.python.org/ftp/python/${python_version}/Python-${python_version}.tgz
    tar zxfv Python-${python_version}.tgz -C ${packagedir}
    ${packagedir}/Python-${python_version}*
    make clean
    ./configure --prefix=${installdir}/python/Python-${python_version} \
                --enable-optimizations \
                --with-lto \
                --with-system-ffi \
                --with-computed-gotos \
                --enable-loadable-sqlite-extensions \
                --with-ensurepip=install \
                --includedir=${installdir}/include \
                --with-system-ffi \
                --with-openssl=${installdir} \
                CFLAGS="-I${installdir}/include" \
                CPPFLAGS="-I${installdir}/include" \
                LDFLAGS="-L${installdir}/lib -L${installdir}/lib64" \
                PKG_CONFIG_LIBDIR="-L${installdir}/lib/pkgconfig"
    make -j${threads}
    make altinstall
        # update PATH
        # export: LD_LIBRARY_PATH=... PATH=...
    python -m ensurepip --upgrade