How to extract the input file offset of a byte in idapython?

Question

For every selected byte Ida Pro displays the offset in the input file where the byte can be found (displayed in the buttom bar of the Ida-View and the Hex-View). How can I retrieve this information when using the idapython API?

Answer 1

When looking for functions, you should always check the SDK headers. These two are listed in loader.hpp:

// Get offset in the input file which corresponds to the given ea
// If the specified ea can't be mapped into the input file offset,
// return -1.    
idaman int32 ida_export get_fileregion_offset(ea_t ea);    

// Get linear address which corresponds to the specified input file offset.
// If can't be found, then return BADADDR    
idaman ea_t ida_export get_fileregion_ea(int32 offset);

So you can use them from IDAPython like this:

offset = idaapi.get_fileregion_offset(ea)
ea = idaapi.get_fileregion_ea(offset)

NB: not all SDK functions are exposed in Python. If you absolutely need something which is only available in C API, you can use ctypes to call it.