how to get bit info

[Back9]

Hi,

I have one byte data and want to know each bit info,
I mean how I can know each bit is set or not?

TIA

 

[Tim Lesher]

Hi,

I have one byte data and want to know each bit info,
I mean how I can know each bit is set or not?

You want the bitwise-and operator, &.

For example, to check the least significant bit, bitwise-and with 1:
0

 

[Laurent Verweijen]

Op donderdag 17-06-2010 om 12:51 uur [tijdzone -0700], schreef Back9:

Hi,

I have one byte data and want to know each bit info,
I mean how I can know each bit is set or not?

TIA

def bitset(x, n):
"""Return whether nth bit of x was set"""
return bool(x & (1 << n))

 

[Irmen de Jong]

Hi,

I have one byte data and want to know each bit info,
I mean how I can know each bit is set or not?

TIA

Use bitwise and, for instance, to see if the third bit is set:

byte = 0b11111111
if byte & 0b00000100:
print "bit is set"

-irmen

 

[Stephen Hansen]

I have one byte data and want to know each bit info,
I mean how I can know each bit is set or not?

... print "Bit 1 is set!"
... else:
... print "Bit 1 is not set!"
Bit 1 is set!... byte = byte | BIT_6
... print "Bit 6 wasn't set, BUT NOW IS."
Bit 6 wasn't set, BUT NOW IS.99

(I added 'how to set a specific bit' just cuz)

Basically, those BIT_X lines are creating numbers which have *only* the
specified bit set. Then you do "byte & BIT_X", and that will return 0 if
the byte doesn't have the specified bit in it. You can then set the bit
with "byte | BIT_X", and unset the bit with "byte ^ BIT_X".

--

Stephen Hansen
... Also: Ixokai
... Mail: me+list/python (AT) ixokai (DOT) io
... Blog: http://meh.ixokai.io/


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[Grant Edwards]

....

Basically, those BIT_X lines are creating numbers which have *only* the
specified bit set. Then you do "byte & BIT_X", and that will return 0 if
the byte doesn't have the specified bit in it. You can then set the bit
with "byte | BIT_X", and unset the bit with "byte ^ BIT_X".

Just to clarify, "byte ^ BIT_X" inverts (toggles) bit X.

If you want to make sure bit X is a 0 (which is what people usually
mean by "unset"), you do "byte & ~BIT_X"

 

[Stephen Hansen]

Just to clarify, "byte ^ BIT_X" inverts (toggles) bit X.

If you want to make sure bit X is a 0 (which is what people usually
mean by "unset"), you do "byte & ~BIT_X"

Doh, you're correct. I got so used to the pattern of only ever flipping
the bit off after for some reason I knew it was on, like:

if blah & CONSTANT_A:
do-stuff
blah = blah ^ CONSTANT_A

That I forgot ^ was invert >_>

Ahem! Thanks for the correction.

--

Stephen Hansen
... Also: Ixokai
... Mail: me+list/python (AT) ixokai (DOT) io
... Blog: http://meh.ixokai.io/


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[Anssi Saari]

Hi,

I have one byte data and want to know each bit info,
I mean how I can know each bit is set or not?

Other than the tedious anding, oring and shifting, you can convert
your byte to a string (with function bin) and use normal string
handling functions to check if individual bits are 0 or 1.

String format is also handy if you happen to need to do things like
reversing the bit order or slicing and joining together various bits
from different bytes.

I seem to invariably need to do some bit order reversing when I mess
around with serial data, which is one reason why I like Python.