input: Write a function to generate an RSA public/private key pair and store them in files named 'public.pem' and 'private.pem' respectively. The function should use the `Crypto.PublicKey.RSA` module to generate a 2048-bit key pair.
  assert generate_key_pair.__name__=='generate_key_pair'
  assert type(f.read()).__name__=='str' for f in [open('public.pem', 'r'), open('private.pem', 'r')]
output: def generate_key_pair():
      from Crypto.PublicKey import RSA
      key = RSA.generate(2048)
      with open('private.pem', 'wb') as private_pem:
          private_pem.write(key.export_key('PEM'))
      with open('public.pem', 'wb') as public_pem:
          public_pem.write(key.publickey().export_key('PEM'))