How to slice arrays in a for loop with the slicing indices variable

Question

I want to slice an array of 64 items in eight parts and for that used the following method but it displayed a syntax error

for i in range(8):
    s = slice(8i,(8i+7))
    inparr = cornersort[s]

and

for i in range(8):
    inparr = cornersort[8i,(8i+7)]

Both show the Error message:

 s = slice(8i,(8i+7))
            ^
SyntaxError: invalid syntax

However when I removed the for loop iterable 'i'; the code worked. Please help how to fix this.

It’s not clear what your intention is. Do you want eight times `i`? That would be `8 * i` — Mark, Jun 25 '19 at 14:28
@MarkMeyer looks that way: "I want to slice an array of 64 items in eight parts" — C.Nivs, Jun 25 '19 at 14:32
Thanks a lot! I am a beginner programmer and made this very silly mistake. — Amol Shah, Jun 25 '19 at 17:44

score 0 · Accepted Answer · answered Jun 25 '19 at 14:34

While 8i is a valid mathematical expression, it is not a valid python statement, since the multiplication operation needs to be explicit, not implied:

i = 8

8i # SyntaxError

8*i
64

Furthermore, in variable names, they must not start with a number:

2i = 5
# syntaxError

i2 = 5
# this is fine

So for your loop:

for i in range(8):
    inparr = cornersort[8*i:(8*i+8)]

score 0 · Answer 2 · answered Jun 25 '19 at 14:35

Please find below examples how to slice an array with 64 items into 8 slices of 8 items each. Please note the basic syntax [start:stop] and the slice indices are start <= i < stop, i.e. stop points one item after the slice.

test = list(range(64))

# example 1
for i in range(8):
    print(test[8*i:8*i+8])

# example 2
for i in range(0,64,8):
    print(test[i:i+8])

score 0 · Answer 3 · answered Jun 25 '19 at 14:35

0

You can use range

 for i in range(0, 64, 8):
      # slice arr[i: i + 8]

the result is

answered Jun 25 '19 at 14:35

Chinny84

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How to slice arrays in a for loop with the slicing indices variable

3 Answers3