# Use Python Slice Notation To Reverse A List Easily

2 min readSep 9, 2021

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The aim of this explainer💡 analyzes the reversion of a Python list using slicing `[::-1]`

notation combining notes from StackOverflow and LeetCode.

## 1. instructions

- slicing syntax, in general, utilizing half-open range

`[ <first element to include> : <first element to exclude> : <step> ]`

- positive int in
`<steps>`

is the size of increment from the left to the right of a list - negative int in
`<steps>`

is the size of increment from the right the left of a list (reversed iteration) - only the first colon in
`[:]`

is really required, all of the other fields can be empty - therefore, to make a copy of the list (aka “colon copy”)

`>>> l = [1,2,3,4]`

>>> l[:]

[1, 2, 3, 4]

- to iterate in a reverse order

`>>> l[::-1]`

[4, 3, 2, 1]

- When you use a negative index as either
`<first element to include>`

or`<first element to exclude>`

it is indexing from the back of the list, so`-1`

is the last element,`-2`

is the second to last element, etc.

`>>> l[-1:]`

[4]

- to iterate over 2 items in a reversed order:

`>>> l[::-2]`

[4, 2]

- therefore to reverse an integer, including the validation method against overflow is easy

`class Solution:`

def reverse(self, x: int) -> int:

if x > 0: # handle positive numbers

a = int(str(x)[::-1])

if x <=0: # handle negative numbers

a = -1 * int(str(x*-1)[::-1])

# handle 32 bit overflow

mina = -2**31

maxa = 2**31 - 1

if a not in range(mina, maxa):

return 0

else:

return a