Arrays/Python/CaesarCipher - Revision history

Admin: /* Q R-5.10 Caesar cipher constructor */

2019-03-12T15:57:13Z

Q R-5.10 Caesar cipher constructor

← Older revision		Revision as of 15:57, 12 March 2019
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	==Q R-5.10 Caesar cipher constructor==		==Q R-5.10 Caesar cipher constructor==

	Link: https://charlesreid1.com~~:3000~~/cs/python/src/master/arrays/CaesarCipher.py		Link: https://git.charlesreid1.com/cs/python/src/master/arrays/CaesarCipher.py

	Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets using a list comprehension.		Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets using a list comprehension.

Admin: /* Goodrich Python Chapter 5 Questions */

2017-06-02T21:47:28Z

Goodrich Python Chapter 5 Questions

← Older revision		Revision as of 21:47, 2 June 2017
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	==Q R-5.10 Caesar cipher constructor==		==Q R-5.10 Caesar cipher constructor==

			Link: https://charlesreid1.com:3000/cs/python/src/master/arrays/CaesarCipher.py

	Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets using a list comprehension.		Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets using a list comprehension.

Admin: /* Output */

2017-05-29T04:59:43Z

Output

← Older revision		Revision as of 04:59, 29 May 2017
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	[[Category:Arrays]]		[[Category:Arrays]]
			[[Category:Strings]]

Admin: /* Output */

2017-05-29T04:58:04Z

Output

← Older revision		Revision as of 04:58, 29 May 2017
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	{{~~DataStructureFlag~~}}		{{DataStructuresFlag}}
	~~{{CSFlag}}~~
	[[Category:Arrays]]		[[Category:Arrays]]

Admin: /* Output */

2017-05-29T04:57:27Z

Output

← Older revision		Revision as of 04:57, 29 May 2017
Line 81:		Line 81:
	{{DataStructureFlag}}		{{DataStructureFlag}}
	{{CSFlag}}		{{CSFlag}}
	[[Category:~~Array~~]]		[[Category:Arrays]]

Admin: /* Output */

2017-05-29T04:57:17Z

Output

← Older revision		Revision as of 04:57, 29 May 2017
Line 81:		Line 81:
	{{DataStructureFlag}}		{{DataStructureFlag}}
	{{CSFlag}}		{{CSFlag}}
	[[Category:~~Arrays~~]]		[[Category:Array]]

Admin: /* Output */

2017-05-29T04:57:11Z

Output

← Older revision		Revision as of 04:57, 29 May 2017
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	Decrypted: ALL GAUL IS DIVIDED INTO THREE PARTS		Decrypted: ALL GAUL IS DIVIDED INTO THREE PARTS
	</pre>		</pre>




			{{DataStructureFlag}}
			{{CSFlag}}
			[[Category:Arrays]]

Admin: /* Output */

2017-05-29T04:56:51Z

Output

← Older revision		Revision as of 04:56, 29 May 2017
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	===Output===		===Output===

			<pre>
			$ python3 CaesarCipher.py
			Orig: ALL GAUL IS DIVIDED INTO THREE PARTS
			Secret: DOO JDXO LV GLYLGHG LQWR WKUHH SDUWV
			Decrypted: ALL GAUL IS DIVIDED INTO THREE PARTS
			</pre>

Admin: /* Q R-5.10 Caesar cipher constructor */

2017-05-29T04:56:33Z

Q R-5.10 Caesar cipher constructor

← Older revision		Revision as of 04:56, 29 May 2017
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	<pre>		<pre>
			self._forward = ''.join([chr(ord('A') +((j + shift)%26)) for j in range(26)])
	self._forward = ''.join([chr(ord('A') +((j + shift)%26)) for j in range(26)])		self._backward = ''.join([chr(ord('A')+((j - shift+26)%26)) for j in range(26)])
	self._backward = ''.join([chr(ord('A')+((j - shift+26)%26)) for j in range(26)])
	</pre>		</pre>

Admin: Created page with " =Goodrich Python Chapter 5 Questions= ==Q R-5.10 Caesar cipher constructor== Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets..."

2017-05-29T04:56:19Z

Created page with " =Goodrich Python Chapter 5 Questions= ==Q R-5.10 Caesar cipher constructor== Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets..."

New page

=Goodrich Python Chapter 5 Questions=

==Q R-5.10 Caesar cipher constructor==

Modify the Caesar Cipher object constructor to initialize the offset forward/backward alphabets using a list comprehension.

Here are the two key lines from the constructor:

<pre>

self._forward = ''.join([chr(ord('A') +((j + shift)%26)) for j in range(26)])
self._backward = ''.join([chr(ord('A')+((j - shift+26)%26)) for j in range(26)])
</pre>

The expressions find the offset, beginning at the letter A (note that all strings passed in are made uppercase), that corresponds to the key "shift". Then we're adding (or subtracting) each sequential integer from 1 to 26, mod 26, so that we move in a circle.

Note that this does no error checking for non letter types, or symbols, or any of that. It's pretty awful in that respect, but it's mainly to illustrate list comprehension.

<pre>
$ cat CaesarCipher.py
"""
Goodrich et al
Data Structures in Python
Chapter 5: Array-Based Sequences

Question R-10

Modify Caesar cipher class to have a 2-line constructor:
build the fwd and backward strings using join and the
appropriate list comprehension syntax
"""

class CaesarCipher:
"""Clas for encrypting/decrypting using Caeesar Cipher"""

def __init__(self,shift):
"""Construct Caesar cipher with the given integer shift"""
self._forward = ''.join([chr(ord('A') +((j + shift)%26)) for j in range(26)])
self._backward = ''.join([chr(ord('A')+((j - shift+26)%26)) for j in range(26)])

def encrypt(self,message):
message = message.upper()
return self._transform(message,self._forward)

def decrypt(self,ciphertext):
ciphertext = ciphertext.upper()
return self._transform(ciphertext,self._backward)

def _transform(self,original,code):
msg = list(original)
for k in range(len(msg)):
if(msg[k].isupper()):
j = ord(msg[k]) - ord('A')
msg[k] = code[j]
return ''.join(msg)

if __name__=="__main__":
c = CaesarCipher(3)
msg = "ALL GAUL IS DIVIDED INTO THREE PARTS"

print("Orig: {0}".format(msg))
coded = c.encrypt(msg)
print("Secret: {0}".format(coded))
plain = c.decrypt(coded)
print("Decrypted: {0}".format(plain))
</pre>

===Output===