我正在尝试在ubuntu中安装虚拟环境，但出现此错误：
karan@karan-HP-Notebook:~/Django_Applications/projects/project_1$ sudo apt-get install python3-venv
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
libpython3-stdlib python-pip-whl python3 python3-minimal python3.6-venv
Suggested packages:
python3-doc python3-tk
The following NEW packages will be installed:
python-pip-whl python3-venv python3.6-venv
The following packages will be upgraded:
libpython3-stdlib python3 python3-minimal
3 upgraded, 3 newly installed, 0 to remove and 330 not upgraded.
Need to get 46.0 kB/1,425 kB of archives.
After this operation, 1,671 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Err:1 http://in.archive.ubuntu.com/ubuntu artful-updates/main amd64 python3-minimal amd64 3.6.3-0ubuntu3
404 Not Found [IP: 2403:8940:3:1::f 80]
Err:2 http://in.archive.ubuntu.com/ubuntu artful-updates/main amd64 python3 amd64 3.6.3-0ubuntu3
404 Not Found [IP: 2403:8940:3:1::f 80]
Err:3 http://in.archive.ubuntu.com/ubuntu artful-updates/main amd64 libpython3-stdlib amd64 3.6.3-0ubuntu3
404 Not Found [IP: 2403:8940:3:1::f 80]
Err:4 http://in.archive.ubuntu.com/ubuntu artful/universe amd64 python3.6-venv amd64 3.6.3-1ubuntu1
404 Not Found [IP: 2403:8940:3:1::f 80]
Err:5 http://in.archive.ubuntu.com/ubuntu artful-updates/universe amd64 python3-venv amd64 3.6.3-0ubuntu3
404 Not Found [IP: 2403:8940:3:1::f 80]
E: Failed to fetch http://in.archive.ubuntu.com/ubuntu/pool/main/p/python3-defaults/python3-minimal_3.6.3-0ubuntu3_amd64.deb 404 Not Found [IP: 2403:8940:3:1::f 80]
E: Failed to fetch http://in.archive.ubuntu.com/ubuntu/pool/main/p/python3-defaults/python3_3.6.3-0ubuntu3_amd64.deb 404 Not Found [IP: 2403:8940:3:1::f 80]
E: Failed to fetch http://in.archive.ubuntu.com/ubuntu/pool/main/p/python3-defaults/libpython3-stdlib_3.6.3-0ubuntu3_amd64.deb 404 Not Found [IP: 2403:8940:3:1::f 80]
E: Failed to fetch http://in.archive.ubuntu.com/ubuntu/pool/universe/p/python3.6/python3.6-venv_3.6.3-1ubuntu1_amd64.deb 404 Not Found [IP: 2403:8940:3:1::f 80]
E: Failed to fetch http://in.archive.ubuntu.com/ubuntu/pool/universe/p/python3-defaults/python3-venv_3.6.3-0ubuntu3_amd64.deb 404 Not Found [IP: 2403:8940:3:1::f 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
我该如何解决？为什么会出现此错误？