"A user-defined **function** is a **named sequence** of statements that perform a computation.\n",
"\n",
"Functions provide benefits as they\n",
"\n",
"- make programs easier to comprehend and debug for humans as they give names to the smaller parts of a larger program (i.e., they **modularize** a code base), and\n",
"- eliminate redundancies by allowing **reuse of code**.\n",
"\n",
"Functions are **defined** once with the `def` statement. Then, they may be **called** many times with the call operator `()`.\n",
"\n",
"They may process **parameterized** inputs, **passed** in as **arguments**, and output a **return value**.\n",
"\n",
"Arguments may be passed in by **position** or **keyword**. Some functions may even require **keyword-only** arguments.\n",
"Functions are a special kind of **callables**. Any object that may be **called** with the call operator `()` is a callable. Built-in functions and **constructors** are other kinds of callables.\n",
"\n",
"Core Python can be extended with code from either the **standard library** or **third-party** libraries.\n",
"\n",
"Outside Jupyter notebooks, Python code is put into **modules** that are grouped in **packages**."