Hello vbr, That's EXACTLY what I needed. rstrip is new for me so I'm going to Dr. Google to learn.
On my efforts I was struggling with .pop() but wasn't very successful... Thank you so much, Yehuda On Sat, Jan 2, 2016 at 8:29 PM, Vlastimil Brom <vlastimil.b...@gmail.com> wrote: > 2016-01-02 18:34 GMT+01:00 yehudak . <katye2...@gmail.com>: > [partly edited for bottom posting] > > On Sat, Jan 2, 2016 at 5:24 PM, Vlastimil Brom <vlastimil.b...@gmail.com > > > > wrote: > >> > >> 2016-01-02 14:14 GMT+01:00 yehudak . <katye2...@gmail.com>: > >> > > [...]>> > On Sat, Jan 2, 2016 at 2:44 PM, Vlastimil Brom > >> > <vlastimil.b...@gmail.com> > >> > wrote: > >> >> > >> >> 2016-01-02 12:49 GMT+01:00 <katye2...@gmail.com>: > >> >> > Hi, newbie here! > >> >> > I'm trying to write a python program to find how many trailing > zeros > >> >> > are > >> >> > in 100! (factorial of 100). > >> >> > I used factorial from the math module, but my efforts to continue > >> >> > failed. Please help. > >> >> > > >> >> > Thank you, > >> >> > Yehuda > >> >> > -- > >> >> > https://mail.python.org/mailman/listinfo/python-list > >> >> > >> > [...] > >> > > >> Hi, > >> If you eventually have this as an assignment or other kind of > >> (self)learning task, you would want to approach this with the methods > >> you know, or are supposed to use. > >> For the math context, you may find this explanations useful: > >> http://www.purplemath.com/modules/factzero.htm > >> a rather straightforward python implementation of this seems to be > >> e.g. this recipe: > >> > >> > http://code.activestate.com/recipes/577844-calculate-trailing-zeroes-in-a-factorial/ > >> Note, that you don't need to calculate the value of the factorial > >> itself using this way. > >> If you have problems with following or understanding the code, you may > >> show your own attempts and tell what problems you encounter with your > >> approach. > >> > >> My previous code sample is based on another - "brute-force" approach, > >> the factorial is calculated (e.g. via the math module as you have > >> found), then the integer is converted to a string, afterwards the part > >> of the result consisting only of zeros - at the end of the string is > >> matched with a regular expression and finally the length of it is > >> determined. > >> > >> Regular expressions might be handy, but are not necesarilly elementary > >> stuff for a newcomer in python programming. > >> You can count the trailing zeros in other ways too - as was suggested > >> - you can reverse the string and count from the beginning then, > >> stopping before the first non-zero digit. > >> The most straightforward way could be to loop (characterwise) through > >> the (reversed) string, check each character whether it equals to "0" > >> and stop as soon as there is another digit. > >> > >> hth, > >> vbr > > > > > > vbr, > > I tried using .pop() but could not get what I wanted .Also, I can't see > an > > advantage in reversing the number. > > Would you care to write explicitly the program for me (and probably for > > other too)? > > Brute Force is the style I'm thinking about. > > > > Sorry, but I learn most from viewing the code. > > > > Appreciated, > > Yehuda > > > Hi, > reversing the string would be useful for directly looping over the > string (the interesting zeros would be at the beginning of the > reversed string. > If you use pop() on a list of the digits, the items are taken from the > end of the list by default, hence no reversing is needed. > What problems do you have with this route? (you will need to convert > from the integer result to string, then to list and use pop() and > count the steps until you reach a non-zero digit) > > If you need this kind of soulution (computing the factorial, > converting to string, counting the trailing zero digits), I believe, > the most easily comprehensible version was posted by Tim Chase a bit > earlier. > In the interactive interpreter, with some intermediate steps added, it > can look like this: > > >>> from math import factorial > >>> fact100_int = factorial(100) > >>> fact100_string = str(fact100_int) > >>> fact100_string_without_trailing_zeros = fact100_string.rstrip("0") > >>> len(fact100_string) - len(fact100_string_without_trailing_zeros) > 24 > >>> > > [aditional info on the rstrip method of any string ("abcd" used for > illustration here): ] > >>> print("abcd".rstrip.__doc__) > S.rstrip([chars]) -> str > > Return a copy of the string S with trailing whitespace removed. > If chars is given and not None, remove characters in chars instead. > >>> > > It should be noted that the approaches which involve computing of the > factorial itself have much lower limits on the size compared to the > algorithmic ones, but for the given case both are sufficient. > > hth, > vbr > -- https://mail.python.org/mailman/listinfo/python-list
