文件读取和RE解析

Question

I've a strange behaviour that I don't understand :

If I open my file , I find my bytes , but only once at a time :

f = open('d:\BB.ki', "rb")
f10 = re.findall( b'\x03\x00\x00\x10''(.*?)''\xF7\x00\xF0', f.read() )
print f10
['1BBBAAAABBBBAAAABBBBAAAABBBBAAAA\x00']

f = open('d:\BB.ki', "rb")
f11 = re.findall( b'\x03\x00\x00\x11''(.*?)''\xF7\x00\xF0', f.read() )
print f11
['2AAABBBBAAAABBBBAAAA\x00']

If I try to opening the file and getting severall bytes , I only get the 1st one (f11 is empty )

f = open('d:\BB.ki', "rb")
f10 = re.findall( b'\x03\x00\x00\x10''(.*?)''\xF7\x00\xF0', f.read() )
f11 = re.findall( b'\x03\x00\x00\x11''(.*?)''\xF7\x00\xF0', f.read() )
print f10,f11
['1BBBAAAABBBBAAAABBBBAAAABBBBAAAA\x00'] **[]**

May I use a loop , or something similar ?

Thanks

Answer 1

After you call f.read() there are no more bytes available to be read so a second call to f.read() will return an empty string. Store the result of f.read() instead of reading twice:

s = f.read()
f10 = re.findall( b'\x03\x00\x00\x10''(.*?)''\xF7\x00\xF0', s)
f11 = re.findall( b'\x03\x00\x00\x11''(.*?)''\xF7\x00\xF0', s) 

You may also want to scan the data just a single time, finding both expressions:

matches = re.findall( b'\x03\x00\x00[\x10\x11]''(.*?)''\xF7\x00\xF0', s)

If your file contains the bytes '\\x03\\x00\\x00\\x10\\x03\\x00\\x00\\x11_\\xF7\\x00\\xF0' the method you proposed will find two overlapping matches ( \\x03\\x00\\x00\\x11_ and _ ), whereas the single scan approach finds only a single match.

Answer 2

f.read() consumes the entire file. only f10 will seen.

try this maybe.

 for line in open('d:\BB.ki', "rb").readlines():
    f10 = re.findall( b'\x03\x00\x00\x10''(.*?)''\xF7\x00\xF0', line )
    f11 = re.findall( b'\x03\x00\x00\x11''(.*?)''\xF7\x00\xF0', line )