How to count down in for loop

Question

In Java  I have the following for loop and I am learning Python   for  int index   last-1  index  gt   posn  index--    My question is simple and probably obvious for most of people who are familiar with Python  I would like to code that  for  loop in Python  How can I do this   I tried to do the following   for index in range last-1  posn  -1     I think it should be range last-1  posn   1  -1   Am I right   I am thankful to anyone especially who will explain to me how to understand the indices work in Python

User · Answer

First I recommand you can try use print and observe the action:

for i in range(0, 5, 1):
    print i

the result:

You can understand the function principle. In fact, range scan range is from 0 to 5-1. It equals 0 <= i < 5

When you really understand for-loop in python, I think its time we get back to business. Let's focus your problem.

You want to use a DECREMENT for-loop in python. I suggest a for-loop tutorial for example.

for i in range(5, 0, -1):
    print i

the result:

Thus it can be seen, it equals 5 >= i > 0

You want to implement your java code in python:

for (int index = last-1; index >= posn; index--)

It should code this:

for i in range(last-1, posn-1, -1)

User · Answer

The range function in python has the syntax   range start  end  step   It has the same syntax as python lists where the start is inclusive but the end is exclusive   So if you want to count from 5 to 1  you would use range 5 0 -1  and if you wanted to count from last to posn you would use range last  posn - 1  -1

User · Answer

If you google   quot Count down for loop python quot  you get these  which are pretty accurate  how to loop down in python list  countdown  Loop backwards using indices in Python  I recommend doing minor searches before posting  Also  quot Learn Python The Hard Way quot  is a good place to start

User · Answer

In python  when you have an iterable  usually you iterate without an index   letters    abcdef    or a list  tupple or other iterable for l in letters      print l    If you need to traverse the iterable in reverse order  you would do   for l in letters   -1       print l    When for any reason you need the index  you can use enumerate   for i  l in enumerate letters  start 1    start is 0 by default     print i l    You can enumerate in reverse order too     for i  l in enumerate letters   -1       print i l    ON ANOTHER NOTE     Usually when we traverse an iterable we do it to apply the same procedure or function to each element  In these cases  it is better to use map   If we need to capitilize each letter   map str upper  letters    Or get the Unicode code of each letter   map ord  letters

[python] How to count down in for loop?

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