Python正则表达式不匹配。 我不能应付

Question

why this match does not work ? The problem is with D

import re

A = [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]
B = [0xa8, 0x2c, 0x53, 0x20, 0xca, 0x62, 0x49, 0x13]
C = [0x1A, 0xC4, 0x17, 0x05, 0x47, 0xE8, 0xA3, 0x83]
D = [0x81, 0x63, 0x1f, 0x55, 0xdb, 0x18, 0x2a, 0xab]


for bin_header in [A, B, C, D]:
    bin_str = ''.join(map(chr, bin_header))
    r = re.match(bin_str, bin_str)
    if not r:
        print map(hex, bin_header) # Surprise it prints D

Answer 1

You are trying to match a string with a regular expression, but ignoring the regular expression syntax. Here is your problem:

>>> chr(0x2a)
'*'

The * has special meaning in regular expression syntax. "abc*" the regular expression won't match "abc*" the string (it will match "abcccc" for example).

I suggest you use = or x in y not re.match for this. Passing random bytes to a regular expression isn't a great idea if you don't know that they are all valid characters, or even what the characters are.

Here's an example using in :

import re

A = [0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]
B = [0xa8, 0x2c, 0x53, 0x20, 0xca, 0x62, 0x49, 0x13]
C = [0x1A, 0xC4, 0x17, 0x05, 0x47, 0xE8, 0xA3, 0x83]
D = [0x81, 0x63, 0x1f, 0x55, 0xdb, 0x18, 0x2a, 0xab]


for bin_header in [A, B, C, D]:
    bin_str = ''.join(map(chr, bin_header))
    matches =  bin_str in bin_str
    if not matches:
        print map(hex, bin_header) # Matches all examples.

Even so, constructing strings from unknown byte streams won't play nicely with character encodings, and you should use the correct methods for working with byte sequences.

If you really want to use strings for this, you could represent them as hex strings. As hex strings are only 0-9a-z you could safely use any string or regular expression matching etc.

for bin_header in [A, B, C, D]:
    bin_str = ''.join('%02x' % i for i in bin_header)
    matches =  bin_str in bin_str
    print(bin_str, matches)
    if not matches:
        print map(hex, bin_header)

gives

('ffffffffffffffff', True)
('a82c5320ca624913', True)
('1ac4170547e8a383', True)
('81631f55db182aab', True)