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All particles are expected to have the following fields defined: particle IDs, masses, coordinates, and velocities.   SPH particles are additionally expected to have a smoothing length, density, and internal energy. Support for additional fields not included in the original \textsc{gadget} specification, such as chemical abundances, is easily added.  This section provides Here, we provide  an overview of the design and capabilities of the \code{gadfly} framework, including the \code{Simulation}, \code{Snapshot}, and \code{PartType DataFrame} objects at the core of \code{gadfly} (Section \ref{sec:hierarchy}), the usage of which is demonstrated in Figure \ref{fig:usage_example}. Our approach to file access and intelligent memory management (Section \ref{sec:fileIO}), our handling of unit conversions (Section \ref{sec:units}) and coordinate transformations (Section \ref{sec:coords}), and the included utilities for parallel batch processing (Section \ref{sec:parallel}).