Python hex variable assignment

问题

I'm using a variable to store data that gets sent by a socket. When I assign it in my program it works but when I read it from a file it is treated as a string.

Example:

data = '\x31\x32\x33'

print data

Outputs

123   # <--- this is the result I want when I read from a file to assign data


f = open('datafile')  <--- datafile contains \x31\x32\x33 on one line

data = f.readline()

print data

Outputs

\x31\x32\x33  # <--- wanted it to print 123, not \x31\x32\x33.

回答1:

In Python the string '\x31\x32\x33' is actually only three characters '\x31' is the character with ordinal 0x31 (49), so '\x31' is equivalent to '1'. It sounds like your file actually contains the 12 characters \x31\x32\x33, which is equivalent to the Python string '\\x31\\x32\\x33', where the escaped backslashes represent a single backslash character (this can also be represented with the raw string literal r'\x31\x32\x33').

If you really are sure that this data should be '123', then you need to look at how that file is being written. If that is something you can control then you should address it there so that you don't end up with data consisting of several bytes representing hex escapes.

It is also possible that whatever is writing this data is already using some data-interchange format (similar to JSON), in which case you don't need to change how it is written, you just need to use a decoder for that data-interchange format (like json.loads(), but this isn't JSON).

If somehow neither of the above are really what you want, and you just want to figure out how to convert a string like r'\x31\x32\x33' to '123' in Python, here is how you can do that:

>>> r'\x31\x32\x33'.decode('string_escape')
'123'

Or in Python 3.x:

>>> br'\x31\x32\x33'.decode('unicode_escape')
'123'

edit: Based on comments it looks like you are actually getting hex strings like '313233', to convert a string like that to '123' you can decode using hex:

>>> '313233'.decode('hex')
'123'

Or on Python 3.x:

>>> bytes.fromhex('313233').decode('utf-8')
'123'

回答2:

I might have violated many programming standards here, but the following code works for the given situation

with open('datafile') as f:
    data=f.read()
data=data.lstrip('\\x') #strips the leftmost '\x' so that now string 'data' contains numbers saperated by '\x'
data=data.strip().split('\\x') #now data contains list of numbers
s=''
for d in data:
    s+=chr(int(d,16)) #this converts hex ascii values to respective characters and concatenate to 's'
print s

回答3:

As stated you are doing post processing, it would be easier to handle if the text was "313233" you would then be able to use

data = "313233"    
print data.decode("hex") # this will print '123'

As stated in comments this is for python 2.7, and is deprecated in 3.3. However unless this question is mis-tagged, this will work.

回答4:

Yes, when you do a conversion from a string to an int, you can specify the base of the numbers in the string:

>>> print int("31", 16)
49

>>> chr(49)
'1'

So you should be able to just parse the hex values out of your file and individually convert them to chars.

来源：https://stackoverflow.com/questions/21465969/python-hex-variable-assignment

标签

python-2.7