MAINT: Updated f-string method (#6230)

* MAINT: Used f-string method

Updated the code with f-string methods wherever required for a better and cleaner understanding of the code.

* Updated files with f-string method

* Update rsa_key_generator.py

* Update rsa_key_generator.py

* Update elgamal_key_generator.py

* Update lru_cache.py

I don't think this change is efficient but it might tackle the error as the error was due to using long character lines.

* Update lru_cache.py

* Update lru_cache.py

Co-authored-by: cyai <seriesscar@gmail.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

neural_network/convolution_neural_network.py

@@ -71,7 +71,7 @@ class CNN:
         with open(save_path, "wb") as f:
             pickle.dump(model_dic, f)
 
-        print("Model saved： %s" % save_path)
+        print(f"Model saved： {save_path}")
 
     @classmethod
     def ReadModel(cls, model_path):
@@ -303,7 +303,7 @@ class CNN:
             plt.show()
 
         print("------------------Training Complished---------------------")
-        print((" - - Training epoch: ", rp, "     - - Mse: %.6f" % mse))
+        print((" - - Training epoch: ", rp, f"     - - Mse: {mse:.6f}"))
         if draw_e:
             draw_error()
         return mse