import sys

class X:
   def __init__( it, var ):
      it.var = var
      return

   def show( it ):
      print( f'{it.var = }' )
      try:
         print( f'{var = }' )
      except (NameError):
         sys.stderr.write( '(Should have qualified with the instance object!)\n' )
         raise
      return


X( var = 'value' ).show()

# python3.11 x.py
it.var = 'value'
(Should have qualified with the instance object!)
Traceback (most recent call last):
  File "/home/aa/tmp/python/x.py", line 18, in <module>
    X( var = 'value' ).show()
  File "/home/aa/tmp/python/x.py", line 11, in show
    print( f'{var = }' )
              ^^^
NameError: name 'var' is not defined. Did you mean: 'vars'?