vignere decipher python

# program to implement vigenere cipher decryption
import string

# method that removes symbols, letters, numbers from the message
def remove_ichars(message):
    other_chars = string.punctuation + string.digits + " "
    n_message = "".join([i for i in message if i not in other_chars])
    return n_message


# this method takes string and shiftvalue as input and returns encrypted string as output
def decrypt(original_msg, key):
    index = 0
    original_msg = original_msg.upper()
    original_msg = remove_ichars(original_msg)
    key = key.upper()
    allchars = string.ascii_uppercase
    decrypted_msg = ""

    for letter in original_msg:
        if letter in allchars:
            position = (allchars.index(letter) - allchars.index(key[index]) + 26) % len(allchars)
            decrypted_msg += allchars[position]
            index += 1
            # reset index is greater than length of key
            if index >= len(key):
                index %= len(key)
        else:
            decrypted_msg += letter
            index = 0
    return decrypted_msg


# method that uses the decrypt method and decrypts files by reading the file path and storing the decrypted file on desktop
def decrypt_file(key):
    file_path = input("Enter File path : ")
    try:
        file1 = open(file_path, 'r+')
        f2 = open("C:/Users/MOHIT/Desktop/decrypted_file.txt", 'w')
        print("File opened Successfully!!")
        file_data = file1.read()
        print("File read Successfully!!")
        decrypted_data = decrypt(file_data, key)
        f2.write(decrypted_data)
        print("Decrypted File stored on Desktop successfully!!")

    except Exception as e:
        print("Problems with opening the file")
        print(str(e))

## main function

# encrypt("hello my name is mohit" , 3)
print("Program to implement Ceasar Cipher decryption")
key = input("Enter the Decryption Key : ")
decrypt_file(key)
# print(decrypt(data, key))

'''

Program to implement Ceasar Cipher decryption
Enter File path : F:/python_3.4/sample.txt
File opened Successfully!!
File read Successfully!!
Decrypted File stored on Desktop successfully!!

'''