Problem set 4: the Caesar Cipher

Getting Started 

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ps4-psuedo.txt: For problems 2a and 4a. 

•

 

ps4.py: the skeleton you’ll fill in 

•

 

words.txt: a list of English words 

•

 

fable.txt: an encoded fable 

Run the code without making any modifications to it, in order to ensure that everything is set up 

correctly. The code that we have given you loads a list of words from a file. If everything is 

okay, after a small delay, you should see the following printed out: 

Loading word list from file... 

55902 words loaded. 

If you see an IOError instead (e.g., No such file or directory), you should change the value of the 

WORDLIST_FILENAME constant (defined near the top of the file) to the complete pathname 

for the file words.txt (this will vary based on where you saved the file). 

The file, ps4.py, has a few functions already implemented that you can use while writing up your 

solution. You can ignore the code between the following comments, though you should read and 

understand everything else: 

 

# ----------------------------------- 

# Helper code 

# (you don't need to understand this helper code) 

. . . 

# (end of helper code) 

# ----------------------------------- 

Pseudocode 

Pseudocode is writing out the algorithm/solution in a form that is like code, but not quite code. 

Pseudocode is language independent, uses plain English (or your native language), and is readily 

understandable. 

Algorithm related articles

 in wikipedia often use pseudocode to explain the 

algorithm. 

Think of writing pseudocode like you would explain it to another person – it doesn’t generally 

have to conform to any particular syntax as long as what’s happening is clear to the grader.  

Pseudocode

 is a compact and informal high-level description of a 

computer programming

 

algorithm

 that uses the structural conventions of a 

programming language

, but is intended for 

human reading rather than machine reading. Pseudocode typically omits details that are not 

essential for human understanding of the algorithm, such as 

variable declarations

, system-

specific code and 

subroutines

. The purpose of using pseudocode is that it is easier for humans to 

understand than conventional programming language code, and that it is a compact and 

---

environment-independent description of the key principles of an algorithm. No standard for 

pseudocode syntax exists, as a program in pseudocode is not an executable program. – 

wikipedia

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