Switch from python3 to python2

Using virtualenv

lut@lut-X405UA:~/anaconda3/bin$ virtualenv -p /usr/bin/python2.7 pyenv
Running virtualenv with interpreter /usr/bin/python2.7
New python executable in /home/lucient/anaconda3/bin/pyenv/bin/python2.7
Also creating executable in /home/lucient/anaconda3/bin/pyenv/bin/python
Installing setuptools, pip, wheel...done.

source ~/anaconda3/bin/pyenv/bin/activate
(pyenv) lut@lut-X405UA:~/anaconda3/bin/pyenv$ repo init -u https://aosp.tuna.tsinghua.edu.cn/platform/manifest
gpg: keyring `/home/lucient/.repoconfig/gnupg/secring.gpg' created
gpg: keyring `/home/lucient/.repoconfig/gnupg/pubring.gpg' created
gpg: /home/lucient/.repoconfig/gnupg/trustdb.gpg: trustdb created
gpg: key 920F5C65: public key "Repo Maintainer " imported
gpg: key 692B382C: public key "Conley Owens " imported
gpg: Total number processed: 2
gpg:               imported: 2  (RSA: 1)