Object reference in Dict - not resolved at runtime

[benthomson]

Here is my code:

total_runtime = None
mail_pfx = "dVDS FULL5 CN"

mail_subj = {
	'completed' : f"{mail_pfx} : [INFO] Refresh completed successfully in: {total_runtime}.",
	'warnissues' : f"{mail_pfx} : [ALERT] Refresh completed with issues in: {total_runtime}"
	}

class Stopwatch():

	def __init__(self):
		self.tick = 0
		self.tock = 0
		self.time = 0

	def start(self):
		self.tick = time.perf_counter()

	def stop(self):
		self.tock = time.perf_counter()
		self.time = timedelta(seconds=math.ceil(self.tock-self.tick))

	def __str__(self):
		return str(self.time)

total_runtime = Stopwatch()
total_runtime.start()
total_runtime.stop()

print(mail_subj['warnissues'])

This is printing "dVDS FULL5 CN : [ALERT] Refresh completed with issues in: None"

I want it to resolve the object at runtime instead of compile time, is there any way to do this?