Posting warning message

[Cameron Simpson]

On 11Jun2018 22:51, Tamara Berger <brgrt2 at gmail.com> wrote:
>On Monday, June 11, 2018 at 7:24:58 PM UTC-4, Gregory Ewing wrote:
>> Tamara Berger wrote:
>> > I typed these 2 lines in the terminal:
>> > 192:~ TamaraB$ sudo python3
>> >>>>python3 -m pip install pytest
>>
>> You need to enter this *single* line in the Terminal:
>>     sudo python3 -m pip install pytest
>>
>> > What does the "-m" stand for in the line of code?
>> It's a cmmand-line option to the python interpreter
>> telling it to execute a module.
>
>Thanks, Greg. But I got a permission error. Here is my command at the prompt and the terminal's response.
>
>192:~ TamaraB$ sudo python3 -m pip install pytest
>Password:
>The directory '/Users/TamaraB/Library/Caches/pip/http' or its parent directory 
>is not owned by the current user and the cache has been disabled. Please check 
>the permissions and owner of that directory. If executing pip with sudo, you 
>may want sudo's -H flag.

sudo leaves the $HOME environment variable unchanged, at least on my Mac. So it 
is using your personal cache directory. And rejecting it becuse it is 
(correctly) owned by you.

>The directory '/Users/TamaraB/Library/Caches/pip' or its parent directory is 
>not owned by the current user and caching wheels has been disabled. check the 
>permissions and owner of that directory. If executing pip with sudo, you may 
>want sudo's -H flag.

Have a look at the sudo command's manual page, by running the command:

  man sudo

In that we can read this:

       -H          The -H (HOME) option option sets the HOME environment
                   variable to the home directory of the target user (root by
                   default) as specified by the password database.  The
                   default handling of the HOME environment variable depends
                   on sudoers(5) settings.  By default, sudo will set HOME if
                   env_reset or always_set_home are set, or if set_home is
                   set and the -s option is specified on the command line.

So the message is a reasonable suggestion, and it is suggesting that you run 
this command:

  sudo -H python3 -m pip install pytest

Regarding the other messages:

>Requirement already satisfied: pytest in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages
>Requirement already satisfied: setuptools in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)
>Requirement already satisfied: pluggy<0.7,>=0.5 in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)
>Requirement already satisfied: atomicwrites>=1.0 in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)
>Requirement already satisfied: more-itertools>=4.0.0 in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)
>Requirement already satisfied: six>=1.10.0 in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)
>Requirement already satisfied: py>=1.5.0 in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)
>Requirement already satisfied: attrs>=17.4.0 in /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (from pytest)

This is all fine - it is just saying that various prerequisites are already 
there.

>You are using pip version 9.0.1, however version 10.0.1 is available.
>You should consider upgrading via the 'pip install --upgrade pip' command.

This is just a suggestion to upgrade pip. Since you're running pip from 
Python's "pip" builtin module this effectively suggests upgrading your Python 3 
install.  Not important or urgent.

>So I'm stuck again. I thought "sudo" was supposed to take care of permissions. 
>Do you have a suggestion?

Sudo isn't magic, and treating it like magic is very common, which is one 
reason I discourage unthinking use of it.

Sudo exists to let your run specific commands as root, the system superuser.  
(It also has modes to run as other users, but root is the default and also the 
most dangerous.)

When you use sudo you have almost unlimited power to change things. This is 
handy for installation activities, and also handy for doing unbound damage to 
the OS install.

I still recommend that you avoid sudo here and use pip's --user option, 
installing the packages in your personal Python tree. It will work just as well 
for almost every purpose and avoid risk to your machine's OS.

Cheers,
Cameron Simpson <cs at cskk.id.au>