Python source code is not executed directly as text. The interpreter first compiles it into bytecode, a compact, lower-level set of instructions for the Python virtual machine, and then executes that bytecode. Compiling takes time, so when a module is imported, CPython saves the bytecode to disk so the next import can skip that step. Those saved files are .pyc files, and they live in a folder called __pycache__ next to the source files.
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