/prog/ challenge V̅MCLXXIV: Dr. Kaprekar

Write the function KaprekarsConstant(num). num parameter being passed will be a 4-digit number with at least two distinct digits. Your program should perform the following routine on the number: Arrange the digits in descending order and, separately, in ascending order (adding leading zeroes to fit it to a 4-digit number), and subtract the smaller of the two resulting numbers from the bigger number. Repeat. Performing this routine will always cause you to reach a fixed number: 6174. Then performing the routine on 6174 will always give you 6174 (7641 - 1467 = 6174). Your program should return the number of times this routine must be performed until 6174 is reached.

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For example: if num is 3524 your program should return 3 because of the following steps:
⁽¹⁾ 5432 - 2345 = 3087,
⁽²) 8730 - 0378 = 8352,
⁽³⁾ 8532 - 2358 = 6174.

Shortest byte count wins. Good luck!

>>15
python doesn't have the pre/post-incrementation syntax:

Python 3.5.2 (default, Nov 23 2017, 16:37:01)
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IPython 2.4.1 -- An enhanced Interactive Python.
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%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.

In [1]: i=0;i++
File "<ipython-input-1-cac78eb7531c>", line 1
i=0;i++
^
SyntaxError: invalid syntax