Slice Functions: Local variable error

Question

In the odds function I keep getting:
UnboundLocalError: local variable 'odds_only' referenced before assignment
Not sure how to fix it.  I keep trying to change things around to test it but I've got nothing.
I got it to work once but it stopped working the second time.  
Any ideas?
```slices.py
def first_4(lst):
    return lst[:4]
def firstandlast_4 (lst2):
    first = lst2 [:4]
    last = lst2 [-4:]
    both = first + last
    return both
def odds (num):
    if len(num) % 2 == 0:
    oddsonly = num [1::2]
    return oddsonly
```

Alexander Davison · Accepted Answer

I think you are a bit lost. The odds function takes in an iterable still, not a number. (It seems that you believe that it takes in an iterable.)
The problem is asking to return an iterable which has all of the odd indexed values from the passed in iterable.
For instance, if I pretended I was within the Python shell:
```python
odds([1, 2, 3, 4, 5])
[2, 4]
odds('abcdefg')
['b', 'd', 'f']
odds((1, 2, 3))
[2]
```
Here's my solution to this problem:
(Let's call the input iterable iter and the output iterable result_iter)
Go through every number from zero to N-1, where N is len(iter). Let's call the "current number" i.
If i is odd, add to result_iter iter[i]. (Because i is an index, not the item itself)
Return result_iter.
Implemented in code, it may look somewhat like this:
python
def odds(iter):
    result_iter = []
    for i in range(len(iter)):
        if i % 2 != 0:
            result_iter.append(iter[i])
    return result_iter

Simpler way for the Pythonista:
python
def odds(iter):
    return [iter[i] for i in range(len(iter)) if i % 2 != 0]

I hope this helps! :grin:
Happy coding! :zap: ~Alex

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Mikaela Land

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Slice Functions: Local variable error

1 Answer

Alexander Davison

Alexander Davison

Mikaela Land

Mikaela Land