[Python-ideas] String interpolation: environment variables, command substitution

[Eric V. Smith]

On 08/26/2015 02:20 PM, Mike Miller wrote:
> One of the remaining questions for the string interpolation subject is
> whether to allow for easy access to environment variables and
> output-capture of external processes (aka command-substitution) as bash
> does.
> 
> While incredibly useful in use-cases such as shell-script replacements,
> the functionality is perceived to be, if not dangerous.  More so than
> arbitrary expressions?  Given that we are talking about string literals
> and not input, I'm not sure, so am looking for feedback.
> 
> The idea is not unheard of in Python, there was a module that captured
> process output called commands in the old days, which was superseded at
> some point by subprocess.check_output() I believe.
> 
> Here is some example syntax modeled on bash, though placed inside
> .format braces.  Note both start with $ as the signal::
> 
>     >>> x'Home folder: {$HOME}'      # environment
>     'Home folder: /home/nobody'
> 
>     >>> x'Files: {$(/bin/ls .)}'     # capture output
>     'foo foo1 foo2'

-1000 for any language syntax that allows access to environment
variables or shell output.

That said, with PEP-498 you can do:

>>> import os
>>> f'HOME={os.environ["HOME"]}'
'HOME=/home/eric'

Which is about as easy as I'd like to make this.

Eric.