如何将字符串转换为字节

Question

I am using python v2.7.3 and am trying to get a conversion to work but am having some issues.

This is code that works the way I would like it to:

testString = "\x00\x13\xA2\x00\x40\xAA\x15\x47"
print 'Test String:',testString 

This produces the following result

TestString: ¢@ªG

Now I load the same string as above along with some other data:

\x00\x13\xA2\x00\x40\xAA\x15\x47123456

into a SQLite3 database and then pull it from the database as such:

cur.execute('select datafield from databasetable')
rows = cur.fetchall()
if len(rows) == 0:
    print 'Sorry Found Nothing!'
else:
    print row[0][:32]

This however produces the following result:

\x00\x13\xA2\x00\x40\xAA\x15\x47

I can not figure out how to convert the database stored string to the bytes string, if that is what it is, as the first snippet of code does. I actually need it to load into a variable in that format so I can pass it to a function for further processing.

The following I have tried:

print "My Addy:",bytes(row[0][:32])
print '{0}'.format(row[0][:32]) 
...

They all produce the same results...

Please

First, Can anyone tell me what format the first results are in? I think its bytes format but am not sure.

Second, How can I convert the database stored text into

Any help and I would be eternally grateful.

Thanks in advance,

Ed

Answer 1

The problem is that you're not storing the value in the database properly. You want to store a sequence of bytes, but you're storing an escaped version of those bytes instead.

When entering string literals into a programming language, you can use escape codes in your source code to access non-printing characters. That's what you've done in your first example:

testString = "\x00\x13\xA2\x00\x40\xAA\x15\x47"
print 'Test String:',testString 

But this is processing done by the Python interpreter as it's reading through your program and executing it.

Change the database column to a binary blob instead of a string, then go back to the code you're using to store the bytes in SQLite3, and have it store the actual bytes ( 'ABC' , 3 bytes) instead of an escaped string ( '\\x41\\x42\\x43' , 12 characters).

If you truly need to store the escaped string in SQLite3 and convert it at run-time, you might be able to use ast.literal_eval() to evaluate it as a string literal.