python01_04.ipynb

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    "# Lesson 04 - Built-In Functions and Help"
   ]
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    "## Questions\n",
    "- How can I find out what built-in functions do?\n",
    "- What kind of errors can occur in a program?\n",
    "\n",
    "## Objectives\n",
    "- Explain the purpose of functions.\n",
    "- Call built-in Python functions.\n",
    "- Use help to display documentation for built-in functions.\n",
    "- Describe situations in which `SyntaxError`s and `NameError`s occur."
   ]
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   "source": [
    "## A Quick Note on Comments\n",
    "- Be sure to use descriptive comments to document your code."
   ]
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    "# This sentence isn't executed by Python\n",
    "adjustment = 0.5 # Neither is this - anything after `#` is ignored."
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    "## Calling Functions\n",
    "- An *argument* is a value that is *passed* to a function.\n",
    "- Functions may take zero or more arguments.\n",
    "- `len()` takes exactly one argument.\n",
    "- `int()`, `str()`, and `float()` create new values from an existing one.\n",
    "- What arguments a function takes depends on how it has been defined.\n",
    "- They key to remember is a function takes zero or more arguments (inputs) and produces some output."
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    "- Even when a function takes zero parameters, you must use parenthesis so Python knows you are calling a function."
   ]
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    "print('before')\n",
    "print()             # Print with no arguments prints a blank line\n",
    "print('after')"
   ]
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    "## Some Common Built-In Functions\n",
    "- `max()` returns the larges value of one or more values.\n",
    "- `min()` returns the smallest.\n",
    "- Both work on character strings as well.\n",
    "  - Both use 0-9, A-Z, and a-z to decide what is large and what is small."
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    "print(max(1, 2, 3))\n",
    "print(min('a', 'A', '0'))"
   ]
  },
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   "source": [
    "## Mixing Arguments\n",
    "- Functions might only work for certain combinations of arguments."
   ]
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   "source": [
    "print(max(1, 'a'))"
   ]
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   "source": [
    "## Default Values\n",
    "- Some functions have pre-defined default values.\n",
    "- `round()` defaults to zero decimal places, but you can specify more explicitly."
   ]
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   "source": [
    "round(3.712)"
   ]
  },
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   "source": [
    "round(3.712, 1)"
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   "source": [
    "## Getting Help\n",
    "- Each function comes with built-in documentation.\n",
    "- Use `help()` to look up how to use a function."
   ]
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   "source": [
    "help(round)"
   ]
  },
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   "metadata": {},
   "source": [
    "- Jupyter notebooks also support clicking on the function and holding <kbd>Shift</kbd>+<kbd>Tab</kbd>."
   ]
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   "source": [
    "## Syntax Errors\n",
    "- If code is typed incorrectly, Python reports a `SytaxError`."
   ]
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  {
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   "source": [
    "# Forgot to close the quote marks around the string\n",
    "name = 'Feng"
   ]
  },
  {
   "cell_type": "code",
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   "source": [
    "# An extra `=` in the assignment\n",
    "age = = 52"
   ]
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  {
   "cell_type": "code",
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   "source": [
    "print('hello world'"
   ]
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    "- Python tries to point out the source of the error with the `^`.\n",
    "- Often the most important part of the error message is the last line.\n",
    "- Do not forget you can Google if an error doesn't make sense."
   ]
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   "source": [
    "## Runtime Errors\n",
    "- Runtime errors (like `NameError`) occur when something goes wrong while the program is running."
   ]
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    "age = 53\n",
    "remaining = 100 - aege  # Spelled 'age' wrong"
   ]
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   "source": [
    "## Every Function Returns Something"
   ]
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   "source": [
    "- Python requires every function to return something.\n",
    "- If a function doesn't return something, Python forces it to return the special datatype `None`."
   ]
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   "source": [
    "result = print('example')\n",
    "print('The result of print is', result)"
   ]
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   "source": [
    "## Exercises\n",
    "\n",
    "**Why don't `max` and `min` return `None` when they are not given arguments? What error message do you get when you try it out?**"
   ]
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    "- Both `max()` and `min()` require at least one argument.\n",
    "- This design means the function throws an error immediately instead of getting an unexpected `None`.\n",
    "- Having an unexpected `None` in a variable may create a runtime error later and be harder to fix."
   ]
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