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   "source": [
    "### <center>San Jose State University<br>Department of Applied Data Science<br><br>**DATA 200<br>Computational Programming for Data Analytics**<br><br>Spring 2024<br>Instructor: Ron Mak</center>"
   ]
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   "source": [
    "# 4.2 Defining Functions"
   ]
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   "metadata": {},
   "source": [
    "#### You've already used some of Python's built-in functions such as `print()`, `int()`, `float()`, `len()`, and `input()`. To distinguish a variable name from a function name, we'll put an empty set of parentheses `()` after a function name, no matter how many parameters the function has."
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   "metadata": {},
   "source": [
    "### Defining a Custom Function"
   ]
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   "metadata": {},
   "source": [
    "#### We can define our own user-defined custom functions. For example, here we define function `square()` which has one parameter named `number`. It returns the square of the value of `number`."
   ]
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   "cell_type": "code",
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   "source": [
    "def square(number):\n",
    "    \"\"\"\n",
    "    Calculate and return the square of number.\n",
    "    \"\"\"\n",
    "    return number*number"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Here are examples of how to call `square()` and display its return value:"
   ]
  },
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   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "square(7)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "square(2.5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "print('The square of 7 is', square(7))"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Returning a Result to a Function’s Caller"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Use the `return` statement to immediately return a value to the function's caller. \n",
    "- #### If there is no expression after the `return` keyword, the function returns the value `None`.\n",
    "- #### If a function completes its execution without executing a `return` statement, the function also returns `None`."
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Specifying a Custom Function’s Docstring "
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Be Pythonic! The first thing after the function header should be a triple-quoted **docstring** that explains:\n",
    "- #### The purpose of the function. What does it do?\n",
    "- #### What each of its parameters are.\n",
    "- #### What does it return.\n",
    "#### The docstring can be one or more lines."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Accessing a Function’s Docstring Via IPython’s Help Mechanism "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "square?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "square??"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### **EXAMPLE:** Define a function `square_root()` that has one parameter and returns the square root of the parameter's value. What is the square root of `6.25`?"
   ]
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   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def square_root(x):\n",
    "    \"\"\"\n",
    "    Return the square root of the value of x.\n",
    "    \"\"\"\n",
    "    return x**0.5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "square_root(6.25)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "##########################################################################\n",
    "# (C) Copyright 2019 by Deitel & Associates, Inc. and                    #\n",
    "# Pearson Education, Inc. All Rights Reserved.                           #\n",
    "#                                                                        #\n",
    "# DISCLAIMER: The authors and publisher of this book have used their     #\n",
    "# best efforts in preparing the book. These efforts include the          #\n",
    "# development, research, and testing of the theories and programs        #\n",
    "# to determine their effectiveness. The authors and publisher make       #\n",
    "# no warranty of any kind, expressed or implied, with regard to these    #\n",
    "# programs or to the documentation contained in these books. The authors #\n",
    "# and publisher shall not be liable in any event for incidental or       #\n",
    "# consequential damages in connection with, or arising out of, the       #\n",
    "# furnishing, performance, or use of these programs.                     #\n",
    "##########################################################################\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Additional material (C) Copyright 2023 by Ronald Mak"
   ]
  }
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