What part are you trying to delay, the expression evaluations, or the
string building part?
There was a recent discussion on python-ideas starting at
https://mail.python.org/archives/list/python-id...@python.org/message/LYAC7JC5253QISKDLRMUCN27GZVIUWZC/
that might interest you.
Eric
On 6/24/2021 5:37 AM, Eric Nieuwland wrote:
In a recent discussion with a colleague we wondered if it would be
possible to postpone the evaluation of an f-string so we could use it
like a regular string and .format() or ‘%’.
I found
https://stackoverflow.com/questions/42497625/how-to-postpone-defer-the-evaluation-of-f-strings
<https://stackoverflow.com/questions/42497625/how-to-postpone-defer-the-evaluation-of-f-strings>
and tweaked it a bit to:
import inspect
class DelayedFString(str):
def __str__(self):
vars = inspect.currentframe().f_back.f_globals.copy()
vars.update(inspect.currentframe().f_back.f_locals)
return self.format(**vars)
delayed_fstring = DelayedFString("The current name is {name}")
# use it inside a function to demonstrate it gets the scoping right
def new_scope():
names = ["foo", "bar"]
for name in names:
print(delayed_fstring)
new_scope()
While this does what it should it is very slow.
So I wondered whether it would be an idea to introduce d-strings
(delayed f-strings) and make f-strings syntactic sugar for
f"The current name is {name}" = str(d"The current name is {name}")
And perhaps access to the variables and conversions specified in the
d-string.
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--
Eric V. Smith
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