I'm struggling to understand this Python code:
```python
old = 0
list1 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
list2 = []
for i in list1:
list2.append(i + old)
old = i
print(list2)
```
The loop goes through `list1`, and `list2` gets updated by adding `i` to the variable `old`. I know what the output is, but I'm confused about how `old` changes with each iteration. Can someone break it down for me?
2 Answers
It's essential to pay attention to how you name your variables. In your code, `old` and `Old` are different variables due to case sensitivity in Python. Make sure you're always using the same casing to avoid confusion! As for debugging, if you're using VSCode, you can set breakpoints and step through your code to see how `old` changes in real time, which might clear things up even more!
The variable `old` holds the last value of `i` from the previous iteration. Basically, during the first loop, `old` starts at 0, so you get `0 + 0` in `list2`. Then, in each subsequent loop, `old` gets updated to the current value of `i`, allowing you to continually add the last value to the current one. It’s like keeping a running total, but using the last number from the previous loop as your starting point! Takes a bit to wrap your head around it, but you’re doing great! 😄
Right! So if you look at the result, each next number is just the sum of the current number and the last one. That’s why you’re seeing those jumping numbers in `list2`. It makes it kind of a cumulative series with some added flair!
Yeah, stepping through can really help visualize what’s happening! You can also check your variable values at each step to see the changes.