Python file writes are buffered, so write() isn't called until the in-memory buffer fills, or the file is closed.
If you can edit the Python script, you should add a flush() after each write, and/or open the file in line-buffered mode
Flush:
f.write(sFileDate + ";" + sHeader)
f.write("\r\n")
f.flush()
Line-buffered mode:
f = open(sFile, "a", buffering=1)