CCing the list. Please use Reply All when responding. > I am still little confused since I was under the impression, > that if a c program was able to write this binary code, > then if we know how c "packed" the data/string then > we able to decode/unpack it using python.
Thats correct but you have to specify the correct decode string to match what C wrote. > Does python not know how c packs the strings? Python knows nothing about what C does its up to the programmer to tell Python how to interpret binary data. So its the programmer who must know how C stores binary strings. > Please help me understand as to why unpack works > for numbers but not for strings. It does work for strings as both Luke and I demonstrated. But you have to tell Python how long the string is. You only specified 's' so Python looked for a single byte string. You needed to specify '4s' for a 4 byte string. Let me put it this way: When you call decode you supply a pattern which struct uses to determine how many bytes it needs and how to assign those bytes to Pyhon data types Python and struct have no idea how those bytes got there they simply take the sequence of bytes and try to interpret them in the way indicated by the format string. Thus if you write an integer into a binary file you will write 4 bytes. Knowing that you can tell struct to decode that as an integer. But you could equally well tell struct to decode those same bytes as 4 characters and struct will do so, because thats what you asked for. The 4 characters will be the ASCII characters with the values of the 4 bytes making up the original number. So the onus is on you, the programmer, to know what the correct decode pattern is for each sequence of bytes read. You can find out what that pattern is and how many bytes it equates to by using things like len(), ord(), hex() etc Youcan see an example of that in my File Handling topic in my tutorial. Look at the section on struct. HTH, Alan G.
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