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Python 3.6: How to expand f-string literals read from a file vs inline statement


On 3/23/18 4:30 AM, Malcolm Greene wrote:
> Looking for advice on how to expand f-string literal strings whose
> values I'm reading from a configuration file vs hard coding into
> my script as statements. I'm using f-strings as a very simple
> template language.
> I'm currently using the following technique to expand these f-strings.
> Is there a better way?
> Bonus if anyone has suggestions on how my expand() function can access
> the locals() value of the caller so this parameter doesn't have to be
> passed in explicitly.
> *def *expand(expression, values):
>
>     """Expand expression using passed in locals()"""
>
>     triple_quote = *"'" ** 3
>     expression = dedent(expression)
>
>     *return *eval(*f'f{triple_quote}{expression}{triple_quote}'*,
>     *None*, values)
>
> product_name = 'Bike ABC'
>
> product_sku = '123456'
>
> product_price = 299.95
>
> discount = 0.85
>
>
>
> # read in product description template
>
> # product_description_template might look like: {product_sku} :
> # {product_name}: ${product_price * discount}product_description_template = config('product_description_template')
>
>
>
> # expand the {expressions} in product_description_template using my
> # locals()product_description = expand(product_description_template, locals())
>
>

Perhaps it doesn't need to be said, but just to be sure: don't use eval 
if you don't trust the people writing the configuration file. They can 
do nearly unlimited damage to your environment.? They are writing code 
that you are running.

--Ned.