No module named pip

I’m not able to “snapcraft” a very simple python snap.

   self._run_pip(setup, download=True)
  File "/snap/snapcraft/794/lib/python3.6/site-packages/snapcraft/plugins/python.py", line 297, in _run_pip
    self._install_pip(download)
  File "/snap/snapcraft/794/lib/python3.6/site-packages/snapcraft/plugins/python.py", line 238, in _install_pip
    pip.download(args)
  File "/snap/snapcraft/794/lib/python3.6/site-packages/snapcraft/plugins/python.py", line 511, in download
    self._exec_func(cmd, env=self._env, **kwargs)
  File "/snap/snapcraft/794/usr/lib/python3.6/subprocess.py", line 291, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['/home/erik/testapp/parts/my-part/install/usr/bin/python3', '-m', 'pip', 'download', '--disable-pip-version-check', '--dest', '/home/erik/testapp/parts/my-part/packages', 'pip', 'setuptools', 'wheel']' returned non-zero exit status 1.
erik@pinky:~/testapp$ /home/erik/testapp/parts/my-part/install/usr/bin/python3 -m pip download --disable-pip-version-check --dest /home/erik/testapp/parts/my-part/packages pip setuptools wheel
/home/erik/testapp/parts/my-part/install/usr/bin/python3: No module named pip

My snapcraft.yaml:

name: app1
version: '0.1' 
summary: Amazing app1
description: |
 Described 

grade: devel # must be 'stable' to release into candidate/stable channels
confinement: devmode # use 'strict' once you have the right plugs and slots

apps:

  app1:
    environment:
      MYVAR: hello
    command: 'app1.py'

parts:

  my-part:
    plugin: python
    source: .
    organize: 
      'app1.py' : bin/
    install: |
      mkdir -p $SNAPCRAFT_PART_INSTALL/bin
      cp app1.py $SNAPCRAFT_PART_INSTALL/bin/

What am I doing wrong?!

erik@pinky:~/Downloads$ snap list
which	Name        Version              Rev   Developer  Notes
charm       2.2.3                114   charms     -
conjure-up  2.5.1-20180106.0201  919   canonical  classic
core        16-2.30              3748  canonical  core
juju        2.3.1                3106  canonical  classic
lxd         2.21                 5408  canonical  -
snapcraft   2.35                 794   canonical  classic
erik@pinky:~/Downloads$ which snapcraft
/snap/bin/snapcraft

Resolution:

sudo pip3 install --upgrade pip