sudo update-alternatives --config python3
There are 2 choices for the alternative python3 (providing /usr/bin/python3).

  Selection    Path                      Priority   Status
------------------------------------------------------------
* 0            /usr/local/bin/python3.7   50        auto mode
  1            /usr/bin/python3.5         40        manual mode
  2            /usr/local/bin/python3.7   50        manual mode

python3 --version
Python 3.7.3

sudo dpkg -i cython3_0.29.2-2_amd64.deb 
(Reading database ... 128889 files and directories currently installed.)
Preparing to unpack cython3_0.29.2-2_amd64.deb ...
Unpacking cython3 (0.29.2-2) over (0.29.2-2) ...
dpkg: dependency problems prevent configuration of cython3:
 cython3 depends on python3 (>= 3.7~); however:
  Version of python3 on system is 3.5.3-1.

dpkg: error processing package cython3 (--install):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 cython3

[ -f /usr/bin/yad ]]
+ DIALOG=yad
+ INFO=image=gtk-dialog-info
+ QUESTION=image=gtk-dialog-question
+ WARNING=image=gtk-dialog-warning
+ ERROR=image=gtk-dialog-error
+ BUTTON0=button
+ BUTTON1=button
+ BUTTON0NUM=:0
+ BUTTON1NUM=:1
+ CENTER=--center
+ [[ -n :0.0 ]]
++ id -u
+ [[ 0 -eq 0 ]]
+ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+ check_grub
+ [[ yes = \y\e\s ]]
+ dpkg -l
+ grep '^ii'
+ grep grub-efi-amd64
+ grep -v bin
+ [[ ! -e /var/lib/dpkg/info/dosfstools.list ]]
+ choose_task
+ [[ yes = \y\e\s ]]
+ uefi_message='uefi enabled'
++ yad '--title=Refracta Snapshot 10.2.10 (20191218)' --center --borders=10 --height 400 --width 426 '--text=This utility wil$[/c]

[c]Choose the first option to create a snapshot.[/c]

[c]This is free software that comes with no warranty or guarantee of any type, including but not limited to express, implied, me$
' --button=OK:0 --button=Help:1 --list --column Num --column 'Choose a task' 01 'Create a snapshot (uefi enabled)' 02 'Re-squ$
+ task='01|Create a snapshot (uefi enabled)|'
+ exit_code=0
+ '[' 0 -ne 0 ']'
+ [[ 01|Create a snapshot (uefi enabled)| =~ 01 ]]
+ please_wait
+ yad --image=gtk-dialog-info '--title=Refracta Snapshot' --center '--text=This may take a moment while the program checks fo$
++ pgrep yad
+ wait_pid=2303
+ check_copies
+ [[ -d /home/snapshot ]]
+ ls '/home/snapshot/*.iso'
ls: cannot access '/home/snapshot/*.iso': No such file or directory
+ snapshot_count=0
++ du -sh /home/snapshot
++ awk '{print $1}'
+ snapshot_size=4.0K
+ [[ -z 4.0K ]]
+ [[ -d /home/work/myfs ]]
++ du -sh /home/work/myfs
++ awk '{ print $1 }'
+ saved_size=9.7G
+ saved_copy='* You have a saved copy of the system using 9.7G of space
  located at /home/work/myfs.'
+ [[ no = \y\e\s ]]
+ save_message='* The temporary copy of the filesystem will be created
at /home/work/myfs and removed when this program finishes.'
+ check_directories
++ echo /home/snapshot
++ awk -F / '{ print "/" $2 "/" $3 }'
++ grep /media/
+ snapdir_is_remote=
++ echo /home/work
++ awk -F / '{ print "/" $2 "/" $3 }'
++ grep /media/
+ workdir_is_remote=
+ '[' -n '' ']'
+ '[' -n '' ']'
+ '[' -n '' ']'
+ '[' -n '' ']'
+ [[ -d /home/snapshot ]]
+ [[ no = \n\o ]]
+ [[ -d /home/work ]]
+ rm -rf /home/work
+ mkdir -p /home/work/iso
+ mkdir -p /home/work/myfs
+ check_space
++ df -h -x tmpfs -x devtmpfs -x iso9660 -x udf -x aufs -x squashfs
++ sed 's/Mounted on/Mountpoint/'
++ awk '{ print  $2 "  \t" $3 "  \t" $4 "  \t" $5 "   \t" $6 "   \t\t\t" $1 }'
+ disk_space='Size      Used    Avail   Use%    Mountpoint                      Filesystem
188G    11G     168G    6%      /                       /dev/sda2
511M    5.3M    506M    2%      /boot/efi                       /dev/sda1'
+ check_initrd
+ echo 'Checking initrd.'
+ lsinitramfs /initrd.img
+ grep -q conf.d/cryptroot
+ lsinitramfs /initrd.img
+ grep -q cryptroot/crypttab
+ remove_cryptroot=yes
+ cryptroot_message='The snapshot initrd will be modified to allow booting the unencrypted snapshot.'
+ lsinitramfs /initrd.img
+ egrep -q 'conf.d/resume|conf.d/zz-resume-auto'
+ remove_resume=yes
+ swap_message='The snapshot initrd will be modified to allow booting without the host'\''s swap partition.'
+ '[' '' = yes ']'
+ kill 2303
+ report_space
++ mktemp /tmp/snapshot-report.XXXX
+ tempfile=/tmp/snapshot-report.RXju
+ echo '
You will need plenty of free space. It is recommended that free space (Avail) in the partition that
holds the work directory (probably "/") should be two times the total installed system size (Used).
(Note: You can deduct the space taken up by previous snapshots and any saved copies of the system from the Used amount.)[/c]

[c]Please CLOSE any running applications NOW.
Turn off NUM LOCK for some laptops.[/c]

[c]* You have 0 snapshots taking up 4.0K of disk space.
* You have a saved copy of the system using 9.7G of space
  located at /home/work/myfs.
* The temporary copy of the filesystem will be created
at /home/work/myfs and removed when this program finishes.
* The snapshot directory is currently set to /home/snapshot[/c]

[c]You can change these and other settings by editing
/etc/refractasnapshot.conf.[/c]

[c]The snapshot initrd will be modified to allow booting the unencrypted snapshot.
The snapshot initrd will be modified to allow booting without the host'\''s swap partition.
Current disk usage:
(For complete listing, exit and run '\''df -h'\'')[/c]

[c]Size    Used    Avail   Use%    Mountpoint                      Filesystem
188G    11G     168G    6%      /                       /dev/sda2
511M    5.3M    506M    2%      /boot/efi                       /dev/sda1'
+ yad --text-info '--title=Status Report' --center --height 400 --width 700 --button=OK:0 --button=Exit:1
+ exit_code=0
+ '[' 0 -ne 0 ']'
+ rm -f /tmp/snapshot-report.RXju
+ set_distro_name
+ [[ /usr/lib/refractasnapshot/iso = \/\u\s\r\/\l\i\b\/\r\e\f\r\a\c\t\a\s\n\a\p\s\h\o\t\/\i\s\o ]]
+ [[ live.cfg = \l\i\v\e\.\c\f\g ]]
++ lsb_release -i -s
+ DISTRO=Debian
++ grep -q Refracta /etc/issue
++ yad --entry '--title=Linux Distribution' --center '--text=This is the distribution name that will appear in the boot menu
for the live image. If it'\''s blank, the menu entries will just say
"GNU/Linux (kernel-version)" ' --entry-text=Debian --width=500 --button=OK:0
+ DISTRO=Debian
+ [[ -z Debian ]]
+ housekeeping
+ [[ '' = \y\e\s ]]
+ [[ -n '' ]]
++ awk -F: '/1000:1000/ { print $1 }' /etc/passwd
+ username=rich
+ [[ rich != user ]]
+ username_opt=username=rich
+ [[ no = \y\e\s ]]
+ [[ -e /vmlinuz ]]
+ [[ -e /initrd.img ]]
+ [[ -n '' ]]
+ [[ -n '' ]]
+ [[ yes = \y\e\s ]]
+ updatedb
/usr/bin/refractasnapshot-gui: line 795: updatedb: command not found
+ tee /dev/fd/63
++ yad '--title=Running updatedb...' --center --progress --pulsate --auto-close --width 300
+ [[ '' = \y\e\s ]]
+ cd /home/work
+ copy_isolinux
+ [[ -f /usr/lib/ISOLINUX/isolinux.bin ]]
+ isolinuxbin=/usr/lib/ISOLINUX/isolinux.bin
+ [[ -f /usr/lib/syslinux/modules/bios/vesamenu.c32 ]]
+ vesamenu=/usr/lib/syslinux/modules/bios/vesamenu.c32
+ rsync -a /usr/lib/syslinux/modules/bios/chain.c32 /usr/lib/refractasnapshot/iso/isolinux/
+ rsync -a /usr/lib/syslinux/modules/bios/ldlinux.c32 /usr/lib/refractasnapshot/iso/isolinux/
+ rsync -a /usr/lib/syslinux/modules/bios/libcom32.c32 /usr/lib/refractasnapshot/iso/isolinux/
+ rsync -a /usr/lib/syslinux/modules/bios/libutil.c32 /usr/lib/refractasnapshot/iso/isolinux/
+ rsync -a /usr/lib/ISOLINUX/isolinux.bin /usr/lib/refractasnapshot/iso/isolinux/
+ rsync -a /usr/lib/syslinux/modules/bios/vesamenu.c32 /usr/lib/refractasnapshot/iso/isolinux/
+ [[ '' = \y\e\s ]]
+ copy_kernel
+ rsync -a /usr/lib/refractasnapshot/iso/ /home/work/iso/
+ cp /vmlinuz /home/work/iso/live/
+ cp /initrd.img /home/work/iso/live/
+ copy_filesystem
+ [[ no = \y\e\s ]]
+ rsync -av / myfs/ --delete-before --delete-excluded --exclude=/home/work --exclude=/home/snapshot --exclude=/home/work/efi-$
+ tee /dev/fd/63
++ yad '--title=Copying filesystem...' --center --progress --pulsate --auto-close --width 300[/c]

[c](yad:3885): GLib-CRITICAL **: 21:15:24.515: g_source_remove: assertion 'tag > 0' failed
+ [[ -n '' ]]
+ '[' yes = yes ']'
+ clean_initrd
+ extract_initrd
+ mkdir /tmp/extracted
mkdir: cannot create directory ‘/tmp/extracted’: File exists
+ pushd /tmp/extracted
++ file -L /initrd.img
++ egrep -o 'gzip compressed|XZ compressed|cpio archive'
+ COMPRESSION='cpio archive'
+ '[' 'cpio archive' = 'gzip compressed' ']'
+ '[' 'cpio archive' = 'XZ compressed' ']'
+ '[' 'cpio archive' = 'cpio archive' ']'
+ echo 'Archive is cpio archive...'
+ cpio -i
cpio: kernel/x86/microcode/AuthenticAMD.bin not created: newer or same age version exists
62 blocks
+ zcat

dsp.alsa.device=default
mixer.alsa.device=default
mixer.alsa.channel=PCM
output_plugin=alsa

sudo refractasnapshot

sent 9,252,418,803 bytes  received 3,037,547 bytes  108,250,951.46 bytes/sec
total size is 9,239,018,468  speedup is 1.00
/tmp/extracted /home/work
Archive is cpio archive...
Decompression error

Squashing the filesystem...
Parallel mksquashfs: Using 12 processors
Creating 4.0 filesystem on iso/live/filesystem.squashfs, block size 131072.
[=========================================================|] 210854/210854 100%

Exportable Squashfs 4.0 filesystem, gzip compressed, data block size 131072
	compressed data, compressed metadata, compressed fragments, compressed xattrs
	duplicates are removed
Filesystem size 3995482.37 Kbytes (3901.84 Mbytes)
	44.22% of uncompressed filesystem size (9034620.15 Kbytes)
Inode table size 1924071 bytes (1878.98 Kbytes)
	29.57% of uncompressed inode table size (6507056 bytes)
Directory table size 1788326 bytes (1746.41 Kbytes)
	38.81% of uncompressed directory table size (4608394 bytes)
Number of duplicate files found 15518
Number of inodes 187909
Number of files 154378
Number of fragments 12073
Number of symbolic links  17760
Number of device nodes 0
Number of fifo nodes 0
Number of socket nodes 0
Number of directories 15771
Number of ids (unique uids + gids) 26
Number of uids 12
	root (0)
	lp (7)
	speech-dispatcher (105)
	rich (1000)
	unknown (501)
	unknown (502)
	unknown (1001)
	unknown (197608)
	colord (108)
	_apt (100)
	man (6)
	geoclue (110)
Number of gids 20
	root (0)
	lp (7)
	shadow (42)
	ssl-cert (105)
	rich (1000)
	staff (50)
	unknown (1001)
	unknown (197121)
	tty (5)
	crontab (102)
	mail (8)
	ssh (106)
	games (60)
	messagebus (104)
	utmp (43)
	lpadmin (108)
	man (12)
	colord (114)
	geoclue (115)
	adm (4)
Creating CD/DVD image file...

	All finished!

"lsb"