Question

I want to encode a set of configuration options into a long string of hex digits.

The input is a mix of numbers (integers and floats) and strings. I can use binascii.a2b_hex from the standard library for the strings, bit-wise operators for the integers, and probably, if I go and read some on floating point representation (sigh), I can probably handle the floats, too.

Now, my questions:

• When given the list of options, (how) should I type check the value to select the correct conversion routine?
• Isn’t there a library function for the numbers, too? I can’t seem to find it.

The serialized data is sent to an embedded device and I have limited control over the code that consumes it (meaning, changes are possible, but a hassle). The specification for the serialization seems to conform to C value representation (char arrays for strings, Little Endian integers, IEEE 754 for floats), but it doesn’t explicitily state this. So, Python-specific stuff like pickle are off-limits.

Answer 1

What about using the struct module to do your packing/unpacking?

import struct
s = struct.pack('S5if',"Hello",42,3.1415)
print s
print struct.unpack('5sif')

or if you really want just hex characters

import struct, binascii
s = binascii.b2a_hex(struct.pack('S5if',"Hello",42,3.1415))
print s
print struct.unpack('5sif',binascii.a2b_hex(s))

Of course this requires that you know the length of strings that are being sent across or you could figure it out by looking for a NULL character or something.