安装了Python 3.7，并尝试将其更改为默认值，但是更改$ PATH并运行python --version仍显示2.7

Question

Sorry if the question is simple or I'm missing something obvious but I'm fairly new with console commands and Python.

As the title suggests, I installed Homebrew and subsequently the latest version of Python. I want to make this the default when running python --version in bash.

I tried changing the path in my bash_profile with the following line at the bottom:

export PATH=/usr/local/bin:/usr/local/sbin:$PATH

It seems that when I install new modules however, that they are for 2.7 and not 3. Checking pip --version going straight to the default:

 pip 18.0 from /usr/local/lib/python2.7/site-packages/pip (python 2.7) 

I also tried running the following commands:

echo "export Path=/usr/local/bin:$PATH" >> ~/.bash_profile && source  ~/.bash_profile

this does edit my bash_profile again, but the line I wanted (and added manually) isn't the one that appears; instead the following is inserted (I have no idea why Applications/VMware is inserted at the end, it has nothing to do with Python or what I'm trying to do):

export PATH=/usr/local/bin:/usr/local/sbin:$PATHexport Path=/usr/local/bin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Applications/VMware

Can anyone explain to me how I can make python3 the default. I don't want to get rid of 2.7 obviously because a lot of scripts for mac still depend on it. Would it be possible to install pipenv and run 3.7 from there, while keeping 2.7 at the default?

Answer 1

You just need to run command

 $which python 

And then goto the path rename python to python2 Then run command

$which python3

To get the path of python3 Just link with command

sudo ln -s $python3path /usr/bin

/python You need to instead $python3path with real path Then you can run python3 with python command

Answer 2

You really don't want to change this.

First:

Would it be possible to install pipenv and run 3.7 from there, while keeping 2.7 at the default?

Yes! Install pipenv , and set up an environment where 3.7 is the default, but leave the system default at 2.7.

---

More generally:

According to PEP 394 , which isn't due to be reevaluated until 2020, if you don't have a virtual environment activated:

• python3 runs Python 3.x
• python2 runs Python 2.x
• python usually shouldn't be used—but if you do use it, it should run Python 2.x.

Usually, you'll also have, eg, python3.7 and python2.7 to run specific 3.x and 2.x versions, although this isn't covered by any standard.

Scripts like pip , and those installed by pip , should be installed with similar suffixes—but ideally, if you have multiple versions, you shouldn't run those scripts. Most of them are designed to be run as modules, so you can run python3 -m pip to run the pip for your 3.x.

For a few things, it may be handy to set up shortcuts. (For example, instead of running python3 -m ipython from the command line, I usually use an iTerm profile that uses that instead of bash as my start command. If you don't use either IPython or iTerm, you can make a Terminal.app profile that runs python3 .)

Scripts installed as part of your platform's package manager are a whole more complicated story, but macOS doesn't have an official package manager, and Homebrew generally expects you to install Python libraries with pip , not brew , so you don't have to worry about that.

Programs should have an installer—whether they install via pip or something like py2app —that creates a proper shbang line, so they run with whichever Python version they were installed with, so you don't have to worry about them. But programs that come with your OS may use something like /usr/bin/env python , and they will expect that to run the version of Python that came with your OS.

For development purposes, you usually want to use virtualenv or pipenv or conda so that python runs the Python interpreter for whichever environment is currently activated.

So, don't try to change the fact that python runs Apple's Python 2.7. That's what it's supposed to do, and if you make it do otherwise, you could break things. Use python3 , python3 -m pip , etc.; use #!/usr/bin/env python3 on your scripts (or, better, use setuptools to create entry-point scripts automatically); use virtual environments; just never run python , and everything will work properly.