[Tutor] Debugging skills (ChatGPT experiment)

[dn]

On 16/01/24 05:16, Mats Wichmann wrote:
...

>> If you come across someone who lands in just such a problem, where 
>> his/her mental model is considerably at-odds with the interpreter; it 
>> would be very interesting to see if/how an LLM helps them through.
>>
>> Alternately, if you can recall such circumstance, I'll be keen to try 
>> to reproduce and to experiment...
> 
> Well, I can name one very simple one:  if you've programmed only in, for 
> example C, your mental model is arrays are pre-allocated (and hopefully 
> you remember the fixed size so you don't go out of bounds), so you might 
> try to use a Python list the same way - the syntax looks similar, after 
> all...
> 
> data = []
> for i in range(5):
>      data[i] = i
> 
> IndexError: list assignment index out of range
> 
> Wait, what?
> 
> Obviously you then quickly learn, so I'm not sure this was a 
> particularly useful example, but the brain wants to follow patterns it 
> knows.


 From ChatGPT 3.5:-


User
You are a Master of programming computers in Python. A trainee's code 
shows the following error:

```python

data = []

for i in range(5):

     data[i] = i

IndexError: list assignment index out of range
```
What is the correct Python idiom to use? Please correct the code.

ChatGPT
Certainly. The issue in the provided code is that you are trying to 
assign values to indices in an empty list, which will result in an 
"IndexError" because the list has no elements initially. To fix this, 
you can use the "append" method to add elements to the list. Here's the 
corrected code:

python
Copy code
data = []

for i in range(5):
     data.append(i)

This way, each iteration of the loop will add the value of i to the end 
of the list, preventing the "IndexError" you encountered.




User
Please re-express the answer in simple terms to suit someone who is just 
starting to learn Python.

ChatGPT
Certainly! In the original code, there was a mistake because the list 
called data was empty, and the code was trying to put values into 
specific positions that didn't exist yet. To fix this, we use the append 
method, which adds elements to the end of the list. Here's the corrected 
version:

python
Copy code
data = []

for i in range(5):
     data.append(i)

Now, it will add each number (i) to the end of the list, and you won't 
encounter the "IndexError" anymore. It's like building the list step by 
step.

User
Why aren't the specific positions available, or at least accessible, 
when create a new list in Python? Having created the list, why not write 
data[ 0 ] = 1?

ChatGPT
When you create a new list in Python, it starts out as an empty list 
with no elements. Unlike some other programming languages, Python 
doesn't automatically allocate space for specific indices when you 
create an empty list. Therefore, if you try to access or assign a value 
to a specific index that doesn't exist yet, you'll encounter an 
"IndexError."

In your original code:

python
Copy code
data = []
for i in range(5):
     data[i] = i

You're attempting to assign values to specific indices (0 to 4) in an 
empty list, but there are no elements at those positions initially.

On the other hand, when you use the append method:

python
Copy code
data = []
for i in range(5):
     data.append(i)

It dynamically adds elements to the end of the list during each 
iteration, avoiding the need to access indices that don't exist. This is 
a common and efficient way to build a list in Python. Once the list is 
populated, you can access specific positions like data[0] = 1 without 
any issues.


Message ChatGPT…

ChatGPT can make mistakes. Consider checking important information.


-- 
Regards,
=dn