On Thu, Feb 24, 2011 at 8:08 AM, Walter Prins <wpr...@gmail.com> wrote:
> > > On 24 February 2011 11:50, tee chwee liong <tc...@hotmail.com> wrote: > >> > int(s,16) for a hex string >> > >> >> great but the leading zeroes are being truncated. >> > > You need to seperate the concept of display/formatting of some thing from > the actual thing/value being displayed. > > Normally when we humans communicate numbers and or work with them, leaading > zero's are not used, so normally most computer systems and languages will > not display numbers with leading zeros by default. It is therefore up to > you to *tell* the computer you want leading zeros in order for it to produce > them from the actual value being represented. > > Furthermore you need to distinguish (as does the computer) between > different object types (namely strings and numbers) as they are different > animals which are handled differently by the computer. > > A number, as already mentioned, will be by default not displayed with > leading zeros as that's normally how humans are used to seeing numbers. > > A string however is a data structure that can contain arbitrary > characters. The computer therefore will generally just display a string > with whatever is in it (some exceptions apply for escape characters etc > depending on context etc. but ignore that for the moment.) > > Now, a string may contain characters that happens to be the character > representation of number (with or without leading zeros) but yet to the > computer this remains a string and only a string, until you *explicitly* > tell it otherwise and explicitly convert it into an actual number object. > After you've done this of course, the computer will know that the thing now > being dealt with is in fact a number, and will therefore display/format the > number as it usually does (e.g. without leading zeros), again, unless you > tell it to display/format it otherwise. > > So at the risk of belaboring the points: 1) Get a handle on the fact that > numbers and strings are different things, and that on the one hand you're > converting between them. 2) Get a handle on the fact that different things > can furthermore be displayed/formatted in a variety of different ways, and > there may be many ways to display or represent a given thing, which again is > up to *you* to control/specify. > > Walter > > > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor > > Take a look at this code. You get your hex number as a string. It has 0x on the left which shows its hexidecimal. Get rid of it with the slice (h[2:] in my example) Now, use the zfill method on the string to pad the result to 5 characters. You can pad to any size you want. Then add back the 0x prefix q.e.d. >>> h = hex(546) >>> h '0x222' >>> n = h[2:] >>> n '222' >>> n.zfill(5) '00222' >>> '0x' + n.zfill(5) '0x00222' >>> This can all be simplified (well .. shortened!) to >>> '0x' + hex(543)[2:].zfill(5) '0x0021f' -- Joel Goldstick
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