I have a fat32 partition image file dump, for example created with dd. how i can parse this file with python and extract the desired file inside this partition.
As far as reading a FAT32 filesystem image in Python goes, the Wikipedia page has all the detail you need to write a read-only implementation.
Construct may be of some use. Looks like they have an example for FAT16 (https://github.com/construct/construct/blob/master/construct/formats/filesystem/fat16.py) which you could try extending.