Python and binary files

The_Nerd · 08-27-2004, 10:22 AM

I need to save bytes, words, dwords, and floats to files using Python in binary format. Then I need to read those values in from the file in C.

Basically I need an "fwrite" for Python, and use "fread" for C. But only "basiaclly".

Help.

P.S. I already wrote functions "FileWriteByte", "FileWriteWord", etc... and they seem to work fine. My only real problem is with "FileWriteFloat". I don't know how to write a floating point number to a file, so I just do a "FileWriteDWord(FloatNum*1000, FileHandle)" and then divide by 1000 in C. So if someone could help me on this then I would be fine. I am just asking abou the others also because I think there might be a better way. Thanks!

deiussum · 08-27-2004, 10:47 AM

I'm by no means a Python expert, but I did something similar for a Python script to export models from Blender into my own custom binary format. Taking a look at my script, I used this code for my "BinaryFileWriter" class:

Code:

class BinaryFileWriter:
    def __init__(self, filename):
        self.__f = file(filename, "wb")
    def WriteByte(self, b):
        self.__f.write(struct.pack('<B', b))
    def WriteUint(self, i):
        self.__f.write(struct.pack('<I', int(i)))
    def WriteString(self, str, size):
        fmt = "<%is" % size
        self.__f.write(struct.pack(fmt, str))
    def WriteFloat(self, f):
        self.__f.write(struct.pack('<f', float(f)))
    def Close(self):
        self.__f.close()

The struct.pack method being one that will get you binary output. I don't remember all the details of struct.pack, so you will probally want to check out the python docs for it as well.

The_Nerd · 08-27-2004, 02:48 PM

Hey thats cool. Thanks!

Btw, this is for a Blender script exporter!

Thats cool that your a Blender user.