string format challenge

[jfc]

My goal is to use the format function to print one value of a dict based on a key known at runtime.
I can do it with the an f-string (first print)
I can do it with a fixed key and the format function (second print)
but I can not do it with a dynamic key and the format function (error)
Is it possible to do this by only modifying the "{self.arr[self.key1]}" part of the third print ?

#!/usr/bin/python3

class Myclass:


   def print(self):
     self.arr={'a1':'v1','a2':'v2'}
     self.key1='a1'

     value1=f"{self.arr[self.key1]}"
     print(value1)

     print("{self.arr[a1]}".format(self=self))

     print("{self.arr[self.key1]}".format(self=self))

Myclass().print()

Output:

Output:
v1
v1

Error:
Traceback (most recent call last):
  File "./ch25-.py", line 17, in <module>
    Myclass().print()
  File "./ch25-.py", line 15, in print
    print("{self.arr[self.key1]}".format(self=self))
KeyError: 'self.key1'