python-intro/solutions/ex14_variable_scope.ipynb

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   "source": [
    "# Exercise 14: Variable Scope"
   ]
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   "source": [
    "## Aim: Learn about local and global variables."
   ]
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    "### Issues covered:\n",
    "- Learn the difference between local and global variables\n",
    "- Make sure to define variables in the right scope\n",
    "- Learn to locate where errors are using the traceback"
   ]
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   "source": [
    "## 1. Let's take a look at local variables"
   ]
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    "What is the problem with the program below? Fix the error to print out the temperature.\n",
    "```\n",
    "change = 1.0\n",
    "\n",
    "def change_temperature(change):\n",
    "    temperature = 100 - change\n",
    "    return temperature\n",
    "\n",
    "print(temperature)\n",
    "```"
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      "99.0\n"
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    "# Temperature is a local variable within the function so you can't access it outside the function.\n",
    "change = 1.0\n",
    "\n",
    "def change_temperature(change):\n",
    "    temperature = 100 - change\n",
    "    return temperature\n",
    "\n",
    "print(change_temperature(change))"
   ]
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   "source": [
    "## 2. Let's investigate the difference between local and global variables."
   ]
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    "Run the block of code below. Do you know why the value of temperature doesn't change? How can you make the value of temperature reflect the changes from the `change_temperature` function?\n",
    "```\n",
    "temperature = 100\n",
    "\n",
    "def change_temperature():\n",
    "    temperature = 0\n",
    "    return temperature\n",
    "\n",
    "print(temperature)\n",
    "change_temperature()\n",
    "print(temperature)\n",
    "```"
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    "# This is the global temperature variable - it is defined outside the function so is visible everywhere\n",
    "temperature = 100\n",
    "\n",
    "def change_temperature():\n",
    "    # This is the local temperature variable\n",
    "    temperature = 0\n",
    "    return temperature\n",
    "\n",
    "# If we set the value of the global temperature variable to the function, it will reflect the changes\n",
    "temperature = change_temperature()\n",
    "print(temperature)"
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   "source": [
    "## 3. Let's take a look at some error messages and learn to understand them"
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    "What is the issue with this block of code? Take a look at the type of error and the error message given.\n",
    "```\n",
    "def print_friday_message():\n",
    "    print_message(\"Friday\")\n",
    "\n",
    "print_friday_message()\n",
    "```"
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    {
     "ename": "NameError",
     "evalue": "name 'print_message' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Input \u001b[0;32mIn [3]\u001b[0m, in \u001b[0;36m<cell line: 4>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mprint_friday_message\u001b[39m():\n\u001b[1;32m      2\u001b[0m     print_message(\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mFriday\u001b[39m\u001b[38;5;124m\"\u001b[39m)\n\u001b[0;32m----> 4\u001b[0m \u001b[43mprint_friday_message\u001b[49m\u001b[43m(\u001b[49m\u001b[43m)\u001b[49m\n",
      "Input \u001b[0;32mIn [3]\u001b[0m, in \u001b[0;36mprint_friday_message\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[38;5;28;01mdef\u001b[39;00m \u001b[38;5;21mprint_friday_message\u001b[39m():\n\u001b[0;32m----> 2\u001b[0m     \u001b[43mprint_message\u001b[49m(\u001b[38;5;124m\"\u001b[39m\u001b[38;5;124mFriday\u001b[39m\u001b[38;5;124m\"\u001b[39m)\n",
      "\u001b[0;31mNameError\u001b[0m: name 'print_message' is not defined"
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    "def print_friday_message():\n",
    "    print_message(\"Friday\")\n",
    "\n",
    "print_friday_message()"
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    "Define a function called `print_message` which has the day as an argument and prints \"Today is <day>\" for any day given. Then write a new function called `print_friday_message` which uses `print_message` to print \"Today is Friday\". Does this run without an error now?"
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     "text": [
      "Today is Friday\n"
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    "# Yes this works now.\n",
    "# Whilst you need to define the functions before you call them, \n",
    "# these don't need to be in any particular order.\n",
    "def print_friday_message():\n",
    "    print_message(\"Friday\")\n",
    "\n",
    "def print_message(day):\n",
    "    print(\"Today is\", day)\n",
    "\n",
    "print_friday_message()"
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