John Cook: Minimizing context switching between shell and Python

Sometimes you’re in the flow using the command line and you’d like to briefly switch over to Python without too much interruption. Or it could be the other way around: you’re in the Python REPL and need to issue a quick shell command.

One solution would be to run your shell and Python session in different terminals, but let’s assume that for whatever reason you’re working in just one terminal. For example, maybe you want the output of a shell command to be visually close when you run Python, or vice versa.

Calling Python from shell

You can run a Python one-liner from the shell by calling Python with the -c option. For example,

    $ python -c "print(3*7)"
    21

I hardly ever do this because I want to run more than a one-liner. What I find more useful is to launch Python with the -q option to suppress all the start-up verbiage and simply bring up a prompt.

    $ python -q
    >>>>

More on this in my post on quiet modes.

Calling shell from Python

If you run Python with the ipython command rather than the default python you get much better shell integration. IPython let’s you type a shell command at any point simply by preceding it with a !. For example, the following command tells us this is the 364th day of the year.

    In [1]: ! date +%j
    364 

You can run some of the most common shell commands, such as cd and ls without even a bang prefix. These are “magic” commands that do what you’d expect if you forgot for a moment that you’re in a Python REPL rather than a command shell.

    In [2]: cd ..
    Out[2]: '/mnt/c/Users'

IPython also supports other forms of shell integration such as capturing the output of a shell command as a Python variable, or using a Python variable as an argument to a shell command.

More on context switching and shells

• Mental context switches are evil
• Advantages of everything-is-text
• Anthony Scopatz on xonsh and shells in general

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