Print a string in binary format
Nick Coghlan
ncoghlan at iinet.net.au
Sat Jan 22 00:59:05 EST 2005
Bengt Richter wrote:
> On Sat, 22 Jan 2005 00:45:19 +1000, Nick Coghlan <ncoghlan at iinet.net.au> wrote:
>>Here's an interesting twiddle, though (there's probably already something along
>>these lines in the cookbook):
>
> Looks like you also played with this problem, after Alex posted a request for alternative
> one-liner solutions to a question on an Italian newsgroup last October? ("show_base" reminded me
> of "number_in_base")
>
> http://groups-beta.google.com/groups?hl=en&lr=&q=number_in_base&qt_s=Search+Groups
See, I knew I wouldn't be the first one to think of it :)
I stole some ideas from that thread to add to the new version down below (I did
not, however, try to make the function expressible as a one-liner, since, after
the function has been defined, *using* it is a one-liner!)
> Hm, learn something every day ;-)
> It didn't occur to me that a string multiplied by a negative number would default
> nicely to the same result as multiplying by zero.
Where'd I learn that trick?. . . oh, that's right, Facundo used it when working
out the string representation for Decimal. It certainly makes padding to a
desired minimum field width pretty easy.
> Of course, this is the prefixed-sign and absolute value representation,
> which is no good if you are using base 2, 8, or 16 to get an idea of
> underlying bits in a negative two-s complement representation.
Dealing with negative numbers isn't really needed for printing a string as
binary , since ord() returns only positive results.
However, we should be able to add complement formatting fairly easily:
Py> def show_base(val, base, min_digits=1, complement=False,
... digits="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"):
... if base > len(digits): raise ValueError("Not enough digits for base")
... negative = val < 0
... val = abs(val)
... if complement:
... sign = ""
... max = base**min_digits
... if (val >= max) or (not negative and val == max):
... raise ValueError("Value out of range for complemented format")
... if negative:
... val = (max - val)
... else:
... sign = "-" * negative
... val_digits = []
... while val:
... val, digit = divmod(val, base)
... val_digits.append(digits[digit])
... result = "".join(reversed(val_digits))
... return sign + ("0" * (min_digits - len(result))) + result
...
Py> show_base(10, 2)
'1010'
Py> show_base(-10, 2)
'-1010'
Py> show_base(10, 2, 8)
'00001010'
Py> show_base(-10, 2, 8)
'-00001010'
Py> show_base(10, 2, 8, complement=True)
'00001010'
Py> show_base(-10, 2, 8, complement=True)
'11110110'
Py> show_base(10, 16, 2, complement=True)
'0A'
Py> show_base(-10, 16, 2, complement=True)
'F6'
Py> show_base(127, 16, 2, complement=True)
'7F'
Py> show_base(-127, 16, 2, complement=True)
'81'
Py> show_base(255, 16, 2, complement=True)
'FF'
Py> show_base(-255, 16, 2, complement=True)
'01'
Py> show_base(256, 16, 2, complement=True)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 10, in show_base
ValueError: Value out of range for complemented format
Py> show_base(-256, 16, 2, complement=True)
'00'
Py>
Cheers,
Nick.
--
Nick Coghlan | ncoghlan at email.com | Brisbane, Australia
---------------------------------------------------------------
http://boredomandlaziness.skystorm.net
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