File Read issue by using module binascii

[Tim Roberts]

Jimmie He <jimmie.he at gmail.com> wrote:

>When I run the readbmp on an example.bmp(about 100k),the Shell is become to "No respose",when I change f.read() to f.read(1000),it is ok,could someone tell me the excat reason for this?
>Thank you in advance!
>
>Python Code as below!!
>
>import binascii
>
>def read_bmp():
>    f = open('example.bmp','rb')
>    rawdata = f.read()                       #f.read(1000) is ok
>    hexstr = binascii.b2a_hex(rawdata)       #Get an HEX number
>    bsstr = bin (int(hexstr,16))[2:]

I suspect the root of the problem here is that you don't understand what
this is actually doing.  You should run this code in the command-line
interpreter, one line at a time, and print the results.

The "read" instruction produces a string with 100k bytes.  The b2a_hex then
produces a string with 200k bytes.  Then, int(hexstr,16) takes that 200,000
byte hex string and converts it to an integer, roughly equal to 10 to the
240,000 power, a number with some 240,000 decimal digits.  You then convert
that integer to a binary string.  That string will contain 800,000 bytes.
You then drop the first two characters and print the other 799,998 bytes,
each of which will be either '0' or '1'.

I am absolutely, positively convinced that's not what you wanted to do.
What point is there in printing out the binary equavalent of a bitmap?

Even if you did, it would be much quicker for you to do the conversion one
byte at a time, completely skipping the conversion to hex and then the
creation of a massive multi-precision number.  Example:

    f = open('example.bmp','rb')
    rawdata = f.read()
    bsstr = []
    for b in rawdata:
        bsstr.append( bin(ord(b)) )
    bsstr = ''.join(bsstr)

or even:
    f = open('example.bmp','rb')
    bsstr = ''.join( bin(ord(b))[2:] for b in f.read() )
-- 
Tim Roberts, timr at probo.com
Providenza & Boekelheide, Inc.