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Python Python Collections (2016, retired 2019) Slices Deleting Or Replacing Slices

neal nakagawa
neal nakagawa
3,409 Points
Posted by neal nakagawa
neal nakagawa
3,409 Points

Why does rainbow[4:5] add to the list and not replace the items in the list at the #4 index? Kenneth's earlier examples

Why does rainbow[4:5] add to the list and not replace the items in the list at the #4 index? Kenneth's earlier examples of [2:4] showed that he replaced ["green","yellow"] with ["yellow","green"].

Chandelor Simon
Chandelor Simon
2,242 Points
Chandelor Simon
Chandelor Simon
2,242 Points

Iulia Maria Lungu is right. I see why you were tripped up though because what's being replaced is included in what it's being replaced with. If you're still iffy on this, think of it this way:

with index 4 of our list(rainbow) still being "blue": if we do rainbow[4:5] = ["cats", "dogs"], then (at this point in the video) when we enter in rainbow, we'd get:

['red', 'orange', 'yellow', 'green', 'cats', 'dogs', 'purple', 'pink']

If index 4 (blue) is x, then we are replacing it with y & z - it just so happens that x = y (blue) in this case scenario.

Gemunu Amarasinghe
Gemunu Amarasinghe
6,991 Points

rainbow[4:5] is one item (include 4, exclude 5). Replace [blue] with [blue, indigo]

rainbow[2:4] is two items (include 2 & 3, exclude 4). Replace [green, yellow] with [yellow, green]

1 Answer

Iulia Maria Lungu
Iulia Maria Lungu
16,935 Points
Iulia Maria Lungu
Iulia Maria Lungu
16,935 Points

I suggest to rewatch the video and pause it. You'll see that doing a rainbow[4:5] = ["blue", "indigo"] does not actually add to the the list, it is a replace that happens as well as when replacing the ["green","yellow"] by ["yellow","green"]. What rainbow[4:5] = ["blue", "indigo"] does is:

  • drop "blue" cause "blue" is at index 4
  • add both "blue" and "indigo"

You thought "indigo" was added but instead truth is "blue" is replaced by "blue", "indigo". Of course what was next to "blue" before now is shifted to the right by one position.