Reading file bit by bit
in [Python]
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From: Alfred Bovin on 7 Jun 2010 04:57 Hi all. I'm working on something where I need to read a (binary) file bit by bit and do something depending on whether the bit is 0 or 1. Any help on doing the actual file reading is appreciated. Thanks in advance
From: Ulrich Eckhardt on 7 Jun 2010 05:12 Alfred Bovin wrote: > I'm working on something where I need to read a (binary) file bit by bit > and do something depending on whether the bit is 0 or 1. Well, smallest unit you can read is an octet/byte. You then check the individual digits of the byte using binary masks. f = open(...) data = f.read() for byte in data: for i in range(8): bit = 2**i & byte ... Uli -- Sator Laser GmbH Geschäftsführer: Thorsten Föcking, Amtsgericht Hamburg HR B62 932
From: Peter Otten on 7 Jun 2010 05:17 Alfred Bovin wrote: > I'm working on something where I need to read a (binary) file bit by bit > and do something depending on whether the bit is 0 or 1. > > Any help on doing the actual file reading is appreciated. The logical unit in which files are written is the byte. You can split the bytes into 8 bits... >>> def bits(f): .... while True: .... b = f.read(1) .... if not b: break .... b = ord(b) .... for i in range(8): .... yield b & 1 .... b >>= 1 .... >>> with open("tmp.dat", "wb") as f: # create a file with some example data .... f.write(chr(0b11001010)+chr(0b10101111)) >>> with open("tmp.dat", "rb") as f: .... for bit in bits(f): .... print bit .... 0 1 0 1 0 0 1 1 1 1 1 1 0 1 0 1 but that's a very inefficient approach. If you explain what you are planning to do we can most certainly come up with a better alternative. Peter
From: Richard Thomas on 7 Jun 2010 05:31 On Jun 7, 10:17 am, Peter Otten <__pete...(a)web.de> wrote: > Alfred Bovin wrote: > > I'm working on something where I need to read a (binary) file bit by bit > > and do something depending on whether the bit is 0 or 1. > > > Any help on doing the actual file reading is appreciated. > > The logical unit in which files are written is the byte. You can split the > bytes into 8 bits... > > >>> def bits(f): > > ... while True: > ... b = f.read(1) > ... if not b: break > ... b = ord(b) > ... for i in range(8): > ... yield b & 1 > ... b >>= 1 > ...>>> with open("tmp.dat", "wb") as f: # create a file with some example data > > ... f.write(chr(0b11001010)+chr(0b10101111))>>> with open("tmp.dat", "rb") as f: > > ... for bit in bits(f): > ... print bit > ... > 0 > 1 > 0 > 1 > 0 > 0 > 1 > 1 > 1 > 1 > 1 > 1 > 0 > 1 > 0 > 1 > > but that's a very inefficient approach. If you explain what you are planning > to do we can most certainly come up with a better alternative. > > Peter You're reading those bits backwards. You want to read the most significant bit of each byte first... Richard.
From: Ulrich Eckhardt on 7 Jun 2010 06:20
Ulrich Eckhardt wrote: > data = f.read() > for byte in data: > for i in range(8): > bit = 2**i & byte > ... Correction: Of course you have to use ord() to get from the single-element string ("byte" above) to its integral value first. Uli -- Sator Laser GmbH Geschäftsführer: Thorsten Föcking, Amtsgericht Hamburg HR B62 932 |