Reading file bit by bit

[Peter Otten]

Richard Thomas wrote:

> On Jun 7, 10:17 am, Peter Otten <__pete... at 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.

>>> def bits(f):
...     while True:
...             byte = f.read(1)
...             if not byte: break
...             byte = ord(byte)
...             for i in reversed(range(8)):
...                     yield byte >> i & 1
...
>>> with open("tmp.dat", "rb") as f:
...     for bit in bits(f):
...             print bit,
...
1 1 0 0 1 0 1 0 1 0 1 0 1 1 1 1