How to reverse the order of tuples in a list

Question

Right now i have list of tuples as show below:

[(78, -32), (54, -32), (30, -32), (30, -8), (30, 16), (30, 40), (30, 64), (6, 64), (-18, 64), (-42, 64), (-66, 64), (-66, 88), (-90, 88), (-114, 88)]

My current codes are as such:

i = 13 # Let i start at index 13
tech = [] # Define list
while (x, y) != (start_x, start_y): # while loop to iterate through all the coordinates until the path has been found
    tech.append(solution[x,y]) # Appends the coordinates to tech list
    x, y = solution[x, y] # get x and y coordinates

for i in tech: # Loop thorugh each tuple
    print(i) # Print each tuple
    # time.sleep(1)
    i -= 1  # Decrement the index

What i want to do is to print out the list in reverse order starting with the last tuple coordinates at the front and the first tuple coordinates at the back. The problem now is that when i try to decrement the index it throws this error:

unsupported operand type(s) for -=: 'tuple' and 'int'

Does anybody know why?

so `[(-114, 88), (-90, 88)], ...`? – Ironkey Nov 10 '20 at 16:03 — Ironkey, Nov 10 '20 at 16:03
`i` is not the index, it's the tuple itself. – Barmar Nov 10 '20 at 16:03 — Barmar, Nov 10 '20 at 16:03
@ Ironkey Yes, that is what im looking for – StackAsker7 Nov 10 '20 at 16:04 — StackAsker7, Nov 10 '20 at 16:04

score 2 · Answer 1 · answered Nov 10 '20 at 16:04

You can use slicing to accomplish this!

x = [(78, -32), (54, -32), (30, -32), (30, -8), (30, 16), (30, 40), (30, 64), (6, 64), (-18, 64), (-42, 64), (-66, 64), (-66, 88), (-90, 88), (-114, 88)]

print(x[::-1])

output

[(-114, 88), (-90, 88), (-66, 88), (-66, 64), (-42, 64), (-18, 64), (6, 64), (30, 64), (30, 40), (30, 16), (30, -8), (30, -32), (54, -32), (78, -32)]

score 1 · Answer 2 · edited Nov 10 '20 at 16:04

1

you can use .reverse() function by doing it:

data= [(78, -32), (54, -32), (30, -32), (30, -8), (30, 16), (30, 40), (30, 64), 
       (6, 64), (-18, 64), (-42, 64), (-66, 64), (-66, 88), (-90, 88), (-114, 88)]
data.reverse()
print(data)

edited Nov 10 '20 at 16:04

Patrick Artner

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answered Nov 10 '20 at 16:03

Jasar Orion

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score 0 · Accepted Answer · answered Nov 10 '20 at 16:04

Here, i is the variable you are using to iterate over the tech list, so decrementing each tuple by 1 doesn't work, if you want to print the items backwards:

print(*reversed(tech),sep="\n")

Reverse in-place :-)

tech.reverse()

Or use a different variable per iteration (Your intent is to decrement i?):

for x in tech: # Loop thorugh each tuple
    print(x) # Print each tuple
    # time.sleep(1)
    i -= 1  # Decrement the index

score 0 · Answer 4 · edited Nov 11 '20 at 03:40

0

l = [(78, -32), (54, -32), (30, -32), (30, -8), (30, 16), (30, 40), (30, 64), (6, 64), (-18, 64), (-42, 64), (-66, 64), (-66, 88), (-90, 88), (-114, 88)]
print(l[::-1])

Using [::-1] will reverse the list values.

edited Nov 11 '20 at 03:40

Joe Ferndz

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answered Nov 10 '20 at 16:06

Code GUI

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Please don't post only code as an answer, but also provide an explanation of what your code does and how it solves the problem of the question. Answers with an explanation are usually more helpful and of better quality, and are more likely to attract upvotes. – Yagiz Degirmenci Nov 10 '20 at 17:01

How to reverse the order of tuples in a list

4 Answers4