python-How to reverse an negative integer or non-integer

Question

I am learning python and I meet some troubles.

I want to write the script to reverse a negative integer " -1234 to 4321- " and non-integer " 1.234 to 432.1". please help me. P.S. cannot use "str()" function

I just only can write the script to reverse positive integer 1234 to 4321

def reverse_int(n):

    x = 0
    while n > 0:
        x *= 10
        x += n % 10
        n /= 10
    return x
print reverse_int(1234)

`4321-` in not a valid number! do you want to convert it to string? — Mazdak, Apr 28 '15 at 17:26
4321- is not a valid integer. How do you plan on representing that as anything other than a string? — derricw, Apr 28 '15 at 17:26
He just said he mustn't use the function `str()`, not that he cannot use strings. Hence, `def reverse_int(n): return '{}'.format(n)[::-1]` should work. — Hyperboreus, Apr 28 '15 at 17:31
I don't understant your script. Could you post details of your solution? — GregMaddux, Apr 28 '15 at 17:35
Hyperboreus' script is just using string substitution using the `format` function, and then reversing the string by using slice notation. — malfunctioning, Apr 28 '15 at 17:42

score 3 · Answer 1 · answered Jul 05 '21 at 14:21

3

def reve(x):
    x=str(x)
    if x[0]=='-':
        a=x[::-1]
        return f"{x[0]}{a[:-1]}"
    else:
        return x[::-1]

print(reve("abc"))
print(reve(123))
print(reve(-123))

#output cba 321 -321

answered Jul 05 '21 at 14:21

Mukund Biradar

141
1
2

2

While this code might answer the OP's question, you could make your answer much better by appending an explanation on how your code solves the problem – Simas Joneliunas Jul 06 '21 at 00:09

score 2 · Accepted Answer · answered Apr 28 '15 at 17:55

2

how about using your code, but just concatenate a - when n is negative?

rev_int.py:

def reverse_int(m):
    x = 0
    n = m
    if m < 0 :
      n *= -1
    while n > 0 :
        x *= 10
        x += n % 10
        n /= 10
    if m < 0:
      #concatenate a - sign at the end
      return `x` + "-"
    return x

print reverse_int(1234)
print reverse_int(-1234)

This produces:

$ python rev_int.py
4321
4321-

answered Apr 28 '15 at 17:55

Curious

2,783
3
29
45

How are you concatenating a string with an integer at `return \`x\` + "-"`? – TigerhawkT3 Apr 28 '15 at 18:04
I can't get this code to work properly for negative numbers, either in Skulpt or in my Python 3 (changing `print` to a function and `/=` to `//=`). – TigerhawkT3 Apr 28 '15 at 18:09
1

How is that any different from using `str()`? You might as well just do `return \`m\`[::-1]`. – TigerhawkT3 Apr 28 '15 at 18:13
@TigerhawkT3 The question is for reversing `integers`, the back ticks convert an integer to string; see [link](http://stackoverflow.com/questions/2847386/python-string-and-integer-concatenation) so the concatenation works. This code would work in Python 2.x, would need change for Python3. Also the question asks NOT to use `str()` – Curious Apr 28 '15 at 18:25
1. I don't think using the syntactic equivalent of `repr()` matches the spirit of the question any better than using `str()`, 2. the question clearly mentions non-integers in both the title and the body, giving an example of `1.234`, and 3. if you're going to use `repr()`/`\`\``, you might as well replace the whole body of the function with `return repr(m)[::-1]`, and then it'll work on Python 2 and 3, for both `int`s and `float`s. – TigerhawkT3 Apr 28 '15 at 18:30
backticks are deprecated, should not be used. http://stackoverflow.com/a/1673087/1860929 – Anshul Goyal May 01 '15 at 06:36

score 0 · Answer 3 · answered Mar 23 '21 at 06:35

0

Using SLICING EASILY DONE IT

def uuu(num):
if num >= 0: 
    return int(str(num)[::-1])
else:
    return int('-{val}'.format(val = str(num)[1:][::-1]))

answered Mar 23 '21 at 06:35

Sunil Chaudhary

1,221
12
25

score 0 · Answer 4 · answered Aug 24 '21 at 17:43

Below code runs fine on Python-3 and handles positive and negative integer case. Below code takes STDIN and prints the output on STDOUT.

Note: below code handles only the integer case and doesn't handles the non-integer case.

def reverseNumber(number):
        x = 0
        #Taking absolute of number for reversion logic
        n = abs(number)
        rev = 0
        #Below logic is to reverse the integer
        while(n > 0):
            a = n % 10
            rev = rev * 10 + a
            n = n // 10
        #Below case handles negative integer case
        if(number < 0):
            return (str(rev) + "-")
        return (rev)
#Takes STDIN input from the user
number=int(input())
#Calls the reverseNumber function and prints the output to STDOUT
print(reverseNumber(number))

score 0 · Answer 5 · answered May 11 '22 at 09:46

0

Using str convert method.

num = 123
print(str(num)[::-1])

answered May 11 '22 at 09:46

Mahesh Chougule

1

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community May 11 '22 at 15:07

smac89 · Answer 6 · 2015-04-28T17:53:17.693

-1

Use this as a guide and make it work for floating point values as well:

import math

def reverse_int(n):
    if abs(n) < 10:
        v = chr(abs(n) + ord('0'))
        if n < 0: v += '-'
        return v
    else:
        x = abs(n) % 10
        if n < 0: return chr(x + ord('0')) + reverse_int(math.ceil(n / 10))
        else: return chr(x + ord('0')) + reverse_int(math.floor(n / 10))

print reverse_int(1234)

edited Apr 28 '15 at 17:53

answered Apr 28 '15 at 17:43

smac89

39,374
15
132
179

output is 40 no matter 1234 or -1234 @@ – GregMaddux Apr 28 '15 at 17:53

score -3 · Answer 7 · edited Oct 15 '22 at 19:12

-3

Why not just do the following?:

def reverse(num):
    revNum = ''
    for i in `num`:
        revNum = i + revNum
    return revNum

print reverse(1.12345)
print reverse(-12345)

These would print 54321.1 and 54321-.

edited Oct 15 '22 at 19:12

miken32

42,008
16
111
154

answered Apr 28 '15 at 18:30

Aaron

1
1

If you wanted simple, you could've copied my `return \`m\`[::-1]` comment exactly instead of adding a loop. And, of course, I don't think `repr()` (what `\`\`` does in Python 2 - `repr()` would be better anyway because it works in 2 and 3) is any better than `str()`. – TigerhawkT3 Apr 28 '15 at 18:46
As written, your script produces 1000000000054321.1 for 1.12345. – Mike Andrews Apr 28 '15 at 18:46

python-How to reverse an negative integer or non-integer

7 Answers7