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# Can string formatting be used to convert an integer to its binaryform ?

Hi,

String formatting can be used to converting an integer to its octal or
>>a = 199
"%o" % a
'307'
>>"%x" % a
'c7'

But, can string formatting be used to convert an integer to its binary
form ?

xiaojf
Sep 28 '06 #1
27 2763
fd********@gmail.com schreef:
Hi,

String formatting can be used to converting an integer to its octal or
>>>a = 199
"%o" % a
'307'
>>>"%x" % a
'c7'

But, can string formatting be used to convert an integer to its binary
form ?

xiaojf
I don't actually know how to do it with string formatting but you can
create a simple function to do it.
Here's an example:
http://aspn.activestate.com/ASPN/Coo.../Recipe/219300

Regards,
Benedict
Sep 28 '06 #2
Thus spoke fd********@gmail.com (on 2006-09-28 09:10):
String formatting can be used to converting an integer to its octal or
>>a = 199
>>"%o" % a
'307'
>>"%x" % a
'c7'

But, can string formatting be used to convert an integer to its binary
form ?
I didn't fell over this problem so far but
I *would* have expected to find something
like a 'pack' operator (as in Perl).

And voilá, there is (even basically identical to Perl):

from struct import *

a = 199
a_bin_str = pack('L', a)

Regards

Mirco
Sep 28 '06 #3
At Thursday 28/9/2006 05:22, Mirco Wahab wrote:
String formatting can be used to converting an integer to its octal or
>>a = 199
>>"%o" % a
'307'
>>"%x" % a
'c7'

But, can string formatting be used to convert an integer to its binary
form ?

a = 199
a_bin_str = pack('L', a)
Notice that the OP was looking for another thing, given the examples.
Perhaps a better wording would have been "how to convert an integer
to its base-2 string representation".
Gabriel Genellina
Softlab SRL

__________________________________________________
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Sep 28 '06 #4
Thus spoke Gabriel Genellina (on 2006-09-28 11:05):
At Thursday 28/9/2006 05:22, Mirco Wahab wrote:
But, can string formatting be used to convert an integer to its binary
form ?

a = 199
a_bin_str = pack('L', a)
>
Notice that the OP was looking for another thing, given the examples.
Perhaps a better wording would have been "how to convert an integer
to its base-2 string representation".
Yes, you are right. The OP looks for a
'binary (bit) representation ..."
I admit I didn't find out how to format
a value into a bit string in Python.

In Perl, this would be a no-brainer:

\$var = 199;
\$str = sprintf "%0*b", 32, \$var;

and str would contain 00000000000000000000000011000111
on a intel machine.

But where is the %b in Python?

Regards & Thanks

Mirco
Sep 28 '06 #5
Mirco Wahab:
But where is the %b in Python?
Python doesn't have that. You can convert the number to a hex, and then
map the hex digitds to binary strings using a dictionary, like this:
http://aspn.activestate.com/ASPN/Coo.../Recipe/440528

Bye,
bearophile

Sep 28 '06 #6
be************@lycos.com wrote:
Mirco Wahab:
>But where is the %b in Python?

Python doesn't have that. You can convert the number to a hex, and then
map the hex digitds to binary strings using a dictionary, like this:
http://aspn.activestate.com/ASPN/Coo.../Recipe/440528

Bye,
bearophile

Good idea, but shorter with ->
http://cheeseshop.python.org/pypi/SE/2.2%20beta
>>import SE
Int_To_Binary = SE.SE (SE.SE ('0=0000 1=0001 2=0010 3=0011 4=0100
5=0101 6=0110 7=0111 8=1000 9=1001 A=1010 a=1010 B=1011 b=1011 C=1100
c=1100 D=1101 d=1101 E=1110 e=1110 F=1111 f=1111')
>>Int_To_Binary ('%x' % 1234567890')
'01001001100101100000001011010010'
>>Int_To_Binary.save ('se_definition_files/int_to_binary.se')
>>SE.SE ('se_definition_files/int_to_binary.se') ('%X' % 987654321)
'00111010110111100110100010110001'
Frederic

Sep 28 '06 #7
Thus spoke Frederic Rentsch (on 2006-09-28 20:43):
be************@lycos.com wrote:
>Mirco Wahab:
>>But where is the %b in Python?

Python doesn't have that. ...
http://aspn.activestate.com/ASPN/Coo.../Recipe/440528

Good idea, but shorter with ->
http://cheeseshop.python.org/pypi/SE/2.2%20beta
SE.SE ('se_definition_files/int_to_binary.se') ('%X' % 987654321)
'00111010110111100110100010110001'
I don't really understand here:

- why doesn't have Python such a simple and useful thing as to_binstr(...)
even C++ has one built in,
#include <iostream>
#include <bitset>

int somefunc()
{
int val = 199;
std::cout << std::bitset<32>( val );
...

- why would you favor such complicated solutions
for this (as posted), when you can have this
in one line, e.g.:

def int2bin(num, width=32):
return ''.join(['%c'%(ord('0')+bool((1<<k)&num)) for k in range((width-1),-1,-1)])

(including a string with specifier,this is what I came up with after
looking up some Python docs - maybe you can straighten this a bit ...)

-- but my goggles might be biased,
I don't really emphasize the "Python way" ;-)

Regards and thanks

Mirco
Sep 28 '06 #8
In <ef**********@mlucom4.urz.uni-halle.de>, Mirco Wahab wrote:
Thus spoke Frederic Rentsch (on 2006-09-28 20:43):
>be************@lycos.com wrote:
>>Mirco Wahab:

But where is the %b in Python?

Python doesn't have that. ...
http://aspn.activestate.com/ASPN/Coo.../Recipe/440528

Good idea, but shorter with ->
http://cheeseshop.python.org/pypi/SE/2.2%20beta
SE.SE ('se_definition_files/int_to_binary.se') ('%X' % 987654321)
'00111010110111100110100010110001'

I don't really understand here:

- why doesn't have Python such a simple and useful thing as to_binstr(...)
Maybe simple, but useful? And if you really need this it's simple to
implement or look up in the cook book.
- why would you favor such complicated solutions
for this (as posted), when you can have this
in one line, e.g.:

def int2bin(num, width=32):
return ''.join(['%c'%(ord('0')+bool((1<<k)&num)) for k in range((width-1),-1,-1)])
Yeah, I wonder why not everybody sees the beauty in this cool and
straightforward one liner. ;-)

Ciao,
Marc 'BlackJack' Rintsch
Sep 28 '06 #9
Mirco Wahab wrote:
- why doesn't have Python such a simple and useful thing as to_binstr(...)
useful? really? for what?

</F>

Sep 28 '06 #10
Thus spoke Marc 'BlackJack' Rintsch (on 2006-09-28 23:38):
> def int2bin(num, width=32):
return ''.join(['%c'%(ord('0')+bool((1<<k)&num)) for k in range((width-1),-1,-1)])

Yeah, I wonder why not everybody sees the beauty in this cool and
straightforward one liner. ;-)
Right. I see this is BS, maybe lots of these lines exist already,
one could come up with (sorted by obfuscation, descending):

def int2bin(num, width=32):
# return ''.join( [chr(ord('0')+bool(1<<k & num))for k in range(width-1,-1,-1)] )
# return ''.join( map(lambda k:str(num>>k & 1),range(width-1, -1, -1)) )
# return ''.join( [str(num>>k & 1)for k in range(width-1, -1, -1)] )

But after some thinking, I thought about discussing this one:

def i2b(num, width):
return str(1 & num>>(width-1)) + i2b(num, width-1) if width else ''

which is the shortest ;-)

(Sorry but I'm more or less a newbie, maybe this is BS too ...)

Regards

Mirco
Sep 28 '06 #11
Thus spoke Fredrik Lundh (on 2006-09-28 23:35):
Mirco Wahab wrote:
>- why doesn't have Python such a simple and useful thing as to_binstr(...)

useful? really? for what?
I don't really know, but according to google,
people often ask exactly for that and there
is no reason at all why one shouldn't expect
to get a /bit string/ from "%b" %.

So if people think it's badly needed, how
couldn't it be *not* useful then? ;-)

It feels to me (as it does sometimes
when diving into Python, to be honest)
simply as a shortcoming, - and the ter-
nary operator included in 2.5 was
imho a huge step forward, next will
be mutable strings and arrays will be
'called arrays' somewhere ... ;-)

(maybe somebody reverses the -v/-V switch too, hey)

Regards

Mirco
Sep 28 '06 #12
Frederic Rentsch:
Good idea, but shorter with ->
>>SE.SE ('se_definition_files/int_to_binary.se') ('%X' % 987654321)
'00111010110111100110100010110001'
Note that your version keeps the leading zeros.
Have you tested the relative speeds too?
(I'll probably have to learn to use SE.)

Bye,
bearophile

Sep 28 '06 #13
In message <11*********************@m7g2000cwm.googlegroups.c om>, be************@lycos.com wrote:
Mirco Wahab:
>But where is the %b in Python?

Python doesn't have that. You can convert the number to a hex, and then
map the hex digitds to binary strings using a dictionary, like this:
http://aspn.activestate.com/ASPN/Coo.../Recipe/440528
How about this: (where n is the integer you want to convert):

"".join([["0", "1"][(1 << i & n) != 0] for i in range(int(math.ceil(math.log(n, 2))) - 1, -1, -1)])

Sep 29 '06 #14
In message <ef**********@lust.ihug.co.nz>, I wrote:
"".join([["0", "1"][(1 << i & n) != 0] for i in range(int(math.ceil(math.log(n, 2))) - 1, -1, -1)])
Uh, make that

"".join([["0", "1"][(1 << i & n) != 0] for i in range(int(math.floor(math.log(n, 2))), -1, -1)])

Need to check those corner cases. :)
Sep 29 '06 #15
At Thursday 28/9/2006 22:07, Lawrence D'Oliveiro wrote:
>How about this: (where n is the integer you want to convert):

"".join([["0", "1"][(1 << i & n) != 0] for i in
range(int(math.ceil(math.log(n, 2))) - 1, -1, -1)])
Uhm... so to generate a binary string you have to import the math
module, convert the integer to float, compute a non-standard
logarithm, and then...
What if n<=0?
Too much, don't you think? :)
Gabriel Genellina
Softlab SRL

__________________________________________________
Preguntá. Respondé. Descubrí.
Todo lo que querías saber, y lo que ni imaginabas,
está en Yahoo! Respuestas (Beta).
¡Probalo ya!
http://www.yahoo.com.ar/respuestas

Sep 29 '06 #16
Gabriel Genellina wrote:
At Thursday 28/9/2006 22:07, Lawrence D'Oliveiro wrote:
How about this: (where n is the integer you want to convert):

"".join([["0", "1"][(1 << i & n) != 0] for i in
range(int(math.ceil(math.log(n, 2))) - 1, -1, -1)])

Uhm... so to generate a binary string you have to import the math
module, convert the integer to float, compute a non-standard
logarithm, and then...
What if n<=0?
Too much, don't you think? :)
Having recently discovered the joy of obfuscated python thanks to the
Code Golf challenges, here's the shortest non-recursive function I came
up with (all integers, signed):

f=lambda n:'-'[:n<0]+''.join(str(m&1)for m in iter(
lambda x=[abs(n)]:(x[0],x.__setitem__(0,x[0]>>1))[0],0))[::-1]or'0'

Any takers ? ;-)

George

Sep 29 '06 #17
So far as unobfuscated versions go, how about the simple:

def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)

Regards,
Jordan

Sep 29 '06 #18
MonkeeSage wrote:
So far as unobfuscated versions go, how about the simple:

def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)

Regards,
Jordan
>>to_bin(0)
''

6/10: try harder :)

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

Sep 29 '06 #19
"MonkeeSage" <Mo********@gmail.comwrites:
def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)
That returns the empty string for x=0. I'm not sure if that's a bug
or a feature.

It also returns the empty string for x < 0, probably a bug.

It will break in Python 3, where 1 / 2 == 0.5.

Here's yet another version:

def to_bin(n):
if n < 0: return '-' + to_bin(-n)
if n==0: return '0'
return ''.join(
("0000", "0001", "0010", "0011",
"0100", "0101", "0110", "0111",
"1000", "1001", "1010", "1011",
"1100", "1101", "1110", "1111",)[int(d,16)] \
for d in '%x'%n).lstrip('0')
Sep 29 '06 #20
Steve Holden wrote:
MonkeeSage wrote:
So far as unobfuscated versions go, how about the simple:

def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)

Regards,
Jordan
>>to_bin(0)
''

6/10: try harder :)
Ok, how about a fast *and* readable version? Works for non-negatives,
but negatives are trivial to add if necessary:

from array import array

def fast2bin(n):
s = array('c')
while n>0:
s.append('01'[n&1])
n >>= 1
s.reverse()
return s.tostring() or '0'

try: import psyco
except ImportError: pass
else: psyco.bind(fast2bin)
George

Sep 29 '06 #21
Steve Holden wrote:
>>to_bin(0)
''
Doh! Oh, yeah...that! ;)

OK...

def to_bin(x):
out=[]
while x 0:
out.insert(0, str(x % 2))
x /= 2
else:
out.append(str(x))
return ''.join(out)

Regards,
Jordan

Sep 29 '06 #22
MonkeeSage wrote:
Steve Holden wrote:
> >>to_bin(0)
''

Doh! Oh, yeah...that! ;)

OK...

def to_bin(x):
out=[]
while x 0:
out.insert(0, str(x % 2))
x /= 2
else:
out.append(str(x))
return ''.join(out)
It's an often-missed and almost invariably untested corner case that
one's first attempt to solve the problem usually rids one of. I have
written binary format code about thirteen times in a lifetime of
programming so it was easy for me to spot. You'll never make *that*
mistake again ;-)

Unfortunately forty years of programming experience has taught me that
there's an essentially infinite supply of mistakes to make ... your
mistakes just get smarter most of the time.

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

Sep 29 '06 #23
be************@lycos.com wrote:
Frederic Rentsch:
>Good idea, but shorter with ->
> >>SE.SE ('se_definition_files/int_to_binary.se') ('%X' % 987654321)
'00111010110111100110100010110001'

Note that your version keeps the leading zeros.
Have you tested the relative speeds too?
(I'll probably have to learn to use SE.)

Bye,
bearophile

If you say speed, I presume you mean speed of execution. No I have not
tested that. I know it can't be fast on a test bench. After all, SE is
written in Python. I did a first version fifteen years ago in C, am
still using it today on occasion and it runs much, much faster than this
Python SE. This SE here could be done in C if it passes the test of
acceptance.
Professionals need to measure execution speed as a part of
documenting their products. I am not a professional and so I am free to
define my own scale of grades: A (fast enough) and F (not fast enough).
I have yet to encounter a situation where SE gets an F. But that says
less about SE than about my better knowledge which prevents me from
using SE to, say, change colors in a 50 Mb bitmap. Obviously, "fast
enough" and "not fast enough" pertains not to code per se, but to code
in a specific situation. So, as the saying goes: the proof of the
pudding ...
Another kind of speed is production speed. I do believe that SE
rather excels on that side. I also believe that the two kinds of speed
are economically related by the return-on-investment principle.
The third kind of speed is learning speed. SE is so simple that it
has no technical learning curve to speak of. It's versatility comes from
a wealth of application techniques that invite exploration, invention
even. Take leading zeroes:

Leading zeroes can be stripped in a second pass if they are made
recognizable in the first pass by some leading mark that is not a zero
or a one. ([^01]; I use "@" in the following example). To purists this
may seem hackish. So it is! And what's wrong with that if it leads to
simpler solutions?
>>Hex_To_Binary = SE.SE ('0=0000 1=0001 2=0010 3=0011 4=0100 5=0101
6=0110 7=0111 8=1000 9=1001 A=1010 a=1010 B=1011 b=1011 C=1100 c=1100
D=1101 d=1101 E=1110 e=1110 F=1111 f=1111 | ~[^01]0*~=')
>>Hex_To_Binary.set (keep_chain = 1)
Hex_To_Binary ('@%x' % 1234567890)
'1001001100101100000001011010010'
>>Hex_To_Binary.show ()
.... snip ...

Data Chain
----------------------------------------------------------------------------------
@499602d2
0
--------------------------------------------------------------------------------
@01001001100101100000001011010010
1
--------------------------------------------------------------------------------
1001001100101100000001011010010
----------------------------------------------------------------------------------
Frederic

(The previously posted example "Int_To_Binary = SE.SE (SE.SE ( ..." was
a typo, or course. One (SE.SE does it. Sorry about that.)

Sep 29 '06 #24
On 9/29/06, Steve Holden <st***@holdenweb.comwrote:
Unfortunately forty years of programming experience has taught me that
there's an essentially infinite supply of mistakes to make ... your
mistakes just get smarter most of the time.
+1 QOTW.

--
Cheers,
Simon B,
si***@brunningonline.net
Sep 29 '06 #25
On 2006-09-29, Steve Holden <st***@holdenweb.comwrote:
MonkeeSage wrote:
>So far as unobfuscated versions go, how about the simple:

def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)

Regards,
It was surprising that
>>i = int("111010101", 2)
is a one-way operation.
>>s = str(i, 2)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: str() takes at most 1 argument (2 given)

--
Neil Cerutti
Sep 29 '06 #26
Neil Cerutti wrote:
On 2006-09-29, Steve Holden <st***@holdenweb.comwrote:
>MonkeeSage wrote:
>>So far as unobfuscated versions go, how about the simple:

def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)

Regards,

It was surprising that
>>>i = int("111010101", 2)

is a one-way operation.
>>>s = str(i, 2)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: str() takes at most 1 argument (2 given)
str() is not only for converting integers, but all other types too.
An explicit argument for this special case is not Pythonic IMO.

Georg
Sep 29 '06 #27
On 2006-09-29, Georg Brandl <g.*************@gmx.netwrote:
Neil Cerutti wrote:
>On 2006-09-29, Steve Holden <st***@holdenweb.comwrote:
>>MonkeeSage wrote:
So far as unobfuscated versions go, how about the simple:

def to_bin(x):
out = []
while x 0:
out.insert(0, str(x % 2))
x = x / 2
return ''.join(out)

Regards,

It was surprising that
>>>>i = int("111010101", 2)

is a one-way operation.
>>>>s = str(i, 2)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: str() takes at most 1 argument (2 given)

str() is not only for converting integers, but all other types
too. An explicit argument for this special case is not Pythonic
IMO.
I suppose two wrongs wouldn't make a right. ;)

--
Neil Cerutti
Sep 29 '06 #28

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