Why am I getting an IndexError from a random choice function?

Question

I am trying to run this code from the beginners' python book Think Python to do Markov Analysis on a text file. When I run the code provided as a solution, I get an IndexError: List index out of range from the random.py module. What do I need to change?

The code should be the answer to Exercise 8 off of Think Python, but I can't get it to work.

Traceback:

Traceback (most recent call last):
  File "test.py", line 115, in <module>
    main(*sys.argv)
  File "test.py", line 111, in main
    random_text(n)
  File "test.py", line 76, in random_text
    start = random.choice(suffix_map.keys())
  File "/Library/Frameworks/EPD64.framework/Versions/7.3/lib/python2.7/random.py", line 274, in choice
    return seq[int(self.random() * len(seq))]  # raises IndexError if seq is empty

Edit: I am running it on a .txt file. It's the text of a book downloaded from Project Gutenburg.

What text file are you running it on? (It has to be run on one with a specific format). — David Robinson, Aug 11 '12 at 21:57
Which text file? Do you have a link? (It must not fit the format I describe in my answer below). — David Robinson, Aug 11 '12 at 22:13

score 0 · Accepted Answer · answered Aug 11 '12 at 22:08

0

The file you are running the program on doesn't have a Gutenberg header. It needs to have a line that starts with:

*END*THE SMALL PRINT!

Only text after that will be read (this occurs in the skip_gutenberg_header function). As an example, running the code on the file

Header info
*END*THE SMALL PRINT!

He was very clever, be it sweetness or be angry, ashamed or only amused, at such a stroke. She had never thought of Hannah till you were never meant for me?" "I cannot make speeches, Emma:" he soon cut it all himself.

produces (as one example):

a stroke. She had never thought of Hannah till you were never meant for me?" "I cannot make speeches, Emma:" he soon cut it all himself. at such a stroke. She had never thought of Hannah till you were never meant for me?" "I cannot make speeches, Emma:" he soon cut it all himself. you were never meant for me?" "I cannot make speeches, Emma:" he soon cut it all himself. cannot make speeches, Emma:" he soon cut it all himself. be it sweetness or be angry, ashamed or only amused, at such a stroke. She had never thought of

answered Aug 11 '12 at 22:08

David Robinson

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You're sure you put the line exactly as it appears in the text? Try commenting out the line where `skip_gutenberg_header` is called. – David Robinson Aug 11 '12 at 22:17
I commented out the call to skip_gutenberg_header and now it works. So it must be a problem with that function. – Cass Aug 11 '12 at 22:18
Is there somewhere I could download the file? – David Robinson Aug 11 '12 at 22:19
Is it possible you either didn't paste in the header line from the start of the line, or didn't save the Python file before running it? It should work if the header signaling file is in there. – David Robinson Aug 11 '12 at 22:20
Also: that line wasn't the last one in the file, was it? It was just the end of the header, right? – David Robinson Aug 11 '12 at 22:21

Why am I getting an IndexError from a random choice function?

1 Answers1