How to implement pre and post increment in Python lists?

Question

In Python how can we increment or decrement an index within the square braces of a list?

For instance, in Java the following code

array[i] = value
i--

can be written as

array[i--]

In Python, how can we implement it? list[i--] is not working

I am currently using

list[i] = value 
i -= 1

Please suggest a concise way of implementing this step.

There's no reasonable way to do this, although of course there's always hacks like defining your own integer class with a 'return the current value and then decrement' method. — Paul Hankin
– Paul Hankin, Commented Jul 24, 2016 at 1:34

Community · Accepted Answer · 2017-05-23 12:14:47Z

8

Python does not have a -- or ++ command. For reasons why, see Why are there no ++ and -- operators in Python?

Your method is idiomatic Python and works fine - I see no reason to change it.

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answered Jul 24, 2016 at 1:36

James

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Comments

Community · Accepted Answer · 2017-05-23 12:00:59Z

4

If what you need is to iterate backwards over a list, this may help you:

>>> a = ["foo", "bar", "baz"]
>>> for i in reversed(a):
...     print i
... 
baz
bar
foo

Or:

for item in my_list[::-1]:
    print item

The first way is how "it should be" in Python.

For more examples:

CommunityBot

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answered Jul 24, 2016 at 1:36

Josemy

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