eppy is a Python library for programmatic manipulation of EnergyPlus input files (IDF) and simulation output. It provides an object-oriented API to read, write, search, modify, and create IDF objects (materials, constructions, zones, HVAC loops, surfaces, etc.), run EnergyPlus simulations from Python, and parse HTML tabular results. The core architecture centers on the `IDF` class (`eppy.modeleditor`) and the `EpBunch` class (`eppy.bunch_subclass`), which represents individual IDF objects with attribute-based field access, type conversion, unit-aware read/write (SI and IP), and automatic extensible field handling. The library also includes subsystems for building geometry calculations (surface area, tilt, azimuth, zone volume), thermal property computations (R-value, U-factor), HVAC loop construction, fan power calculations, and lazy HTML table extraction. Key entry points are `eppy.easyopen.easyopen()` for opening IDF files with automatic IDD detection, `IDF` for full file management, and `run_functions.run()` for simulation execution. External dependencies include EnergyPlus (for running simulations), plus Python packages like beautifulsoup4, lxml, pydot, and pyparsing. While primarily a library for building energy modeling workflows, it also contains reusable data-oriented components (geometry, thermal calculations, unit conversion) that can be applied to other energy simulation or engineering domains. The codebase has some legacy code from early Python 2 days and a high number of open issues, but remains actively developed with ongoing fixes for extensible fields and new EnergyPlus versions.