Python program. Instructions are given within the quotations for each function. 1) def isValidKey(key): """ Returns True if key is a string that has 26 characters and each of the letter 'a'/'A'-'z'/'Z' appeared once and only once in either lower case or upper case. Returns False otherwise. """ 2) def replace(letter, key): """ Assume letter is a single characer string. Replace a single letter with its corresponding key, returns letter if it is not in the alphabet 'a'-'z' or 'A'-'Z' """ 3) def substitution(plainText, key): """ Returns encrypted string for the plainText using substitution encryption, which is to substitute 'a'/'A' with the lower/upper case of key[0], and substitute 'b'/'B' with the lower/upper case of key[1], and so on all the way to 'z'/'Z'. Leave all other non-alpha characters as it is in plainText. Your algorithm should be efficient so that it can run fairly quickly for very large strings. 1. use replace() to convert each letter to its encrypted letter 2. append encrypted letter to a list 3. use ''.join(list_of_letters) to form the final string. Do not use + to do string concatenation to form the encrypted string. """ 4) def run(): """ 1. Prompt user for a key; 2. Check if key is valid. If not, print an error message then return; if valid, prompt for a plain text to be encrypted with the valid key, 3. Send the plain text and valid key to substitution function. 4. Print out the encrypted message. """

C++ for Engineers and Scientists

4th Edition

ISBN:9781133187844

Author:Bronson, Gary J.

Publisher:Bronson, Gary J.

Chapter4: Selection Structures

Section4.3: Nested If Statements

Problem 7E

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Python program. Instructions are given within the quotations for each function.

1) def isValidKey(key):

"""

Returns True if key is a string that has 26 characters and each of the letter

'a'/'A'-'z'/'Z' appeared once and only once in either lower case or upper case.

Returns False otherwise.

"""

2) def replace(letter, key):

"""

Assume letter is a single characer string.

Replace a single letter with its corresponding key, returns letter if it is

not in the alphabet 'a'-'z' or 'A'-'Z'

"""

3) def substitution(plainText, key):

"""

Returns encrypted string for the plainText using substitution encryption, which

is to substitute 'a'/'A' with the lower/upper case of key[0], and substitute

'b'/'B' with the lower/upper case of key[1], and so on all the way to 'z'/'Z'.

Leave all other non-alpha characters as it is in plainText.

Your algorithm should be efficient so that it can run fairly quickly for very

large strings.

1. use replace() to convert each letter to its encrypted letter

2. append encrypted letter to a list

3. use ''.join(list_of_letters) to form the final string. Do not use + to do

string concatenation to form the encrypted string.

"""

4) def run():

"""

1. Prompt user for a key;

2. Check if key is valid. If not, print an error message then return;

if valid, prompt for a plain text to be encrypted with the valid key,

3. Send the plain text and valid key to substitution function.

4. Print out the encrypted message.

"""

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