How useful is The Pianist as an historical reference?
The Pianist is a book (1946) and a film (2002), both based on the life of Jewish composer Wldyslaw Szpilman. The semi-autobiographical story is based on Szpilman's life and experiences during the Nazi invasion of Poland and the horrifying events that followed. I use the term "semi-autobiographical" because Szpilman recounted his memories to a friend who helped him write the book.
When conducting research for a paper or other work, memoirs and (auto)biographies can be problematic as a source. In many cases, the individual has done their best to recall the events as they experienced them, but memory is tricky and can be very subjective. Making matters more complicated, the Pianist has been censored and edited many times over the decades; first by the Russians in the years just after the war and most recently by Szpilman's son, who likely changed very little. As a result, you should be cautious about using the book or the film as a primary source because you have no way of knowing what, if anything has been altered or omitted.
With that disclaimer out of the way, the book (and to a lesser extent the film) does provide a detailed and honest depiction of the events that followed Germany's invasion of Poland. For that reason, Szpilman's autobiography can provide a "big picture" view of the invasion, particularly the often overlooked Warsaw uprising. Nevertheless, if you decide to use this as a source, be sure to verify the information that you choose with information from other sources.