Python将混合的ASCII代码转换为字符串

Question

I am retrieving a value that is set by another application from memcached using python-memcached library. But unfortunately this is the value that I am getting:

>>> mc.get("key")
'\x04\x08"\nHello'

Is it possible to parse this mixed ASCII code into plain string using python function?

Thanks heaps for your help

Answer 1

It is a "plain string", to the extent that such a thing exists. I have no idea what kind of output you're expecting, but:

There ain't no such thing as plain text .

The Python (in 2.x, anyway) str type is really a container for bytes, not characters. So it isn't really text in the first place :) It displays the bytes assuming a very simple encoding, using escape sequence to represent every byte that's even slightly "weird". It will be formatted differently again if you print the string (what you're seeing right now is syntax for creating such a literal string in your code).

In simpler times, we naively assumed that we could just map bytes to these symbols we call "characters", and that would be that. Then it turned out that there were approximately a zillion different mappings that people wanted to use, and lots of them needed more symbols than a byte could represent. Which is why we have Unicode now: it represents every symbol you could conceivably need for any real-world language (and several for fake languages and other purposes), and it abstractly assigns numbers to those symbols but does not say how to collect and interpret the bytes as numbers. (That is the purpose of the encoding).

If you know that the string data is encoded in a particular way, you can decode it to a Unicode string. It could either be an encoding of actual Unicode data, or it could be in some other format (for example, Japanese text is often found in something called "Shift-JIS", because it has approximately the same significance to them as "Latin-1" - a common extension of ASCII - does to us). Either way, you get an in-memory representation of a series of Unicode code points (the numbers referred to in the previous paragraph). This, for all intents and purposes, is really "text", but it isn't really "plain" :)

But it looks like the data you have is really a binary blob of bytes that simply happens to consist mostly of "readable text" if interpreted as ASCII.

What you really need to do is figure out why the first byte has a value of 4 and the next byte has a value of 8, and proceed accordingly.

Answer 2

If you just need to trim the '\\x04\\x08"\\n' , and it's always the same (you haven't put your question very clearly, I'm not certain if that's what it is or what you want), do something like this:

to_trim = '\x04\x08"\n'
string = mc.get('key')
if string.startswith(to_trim):
    string = string[len(to_trim):]