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    "# Conditional statements\n",
    "\n",
    "## Sources\n",
    "This lesson is based on the [Software Carpentry group's](http://software-carpentry.org) lessons on [Programming with Python](http://swcarpentry.github.io/python-novice-inflammation/).\n",
    "\n",
    "## Basics of conditional statements\n",
    "Conditional statements can change the code behavior based on meeting certain conditions.\n",
    "\n",
    "### A starting example\n",
    "\n",
    "Let's take a simple conditional statement example."
   ]
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  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
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   "source": [
    "num = 37\n",
    "if num > 100:\n",
    "    print('greater')\n",
    "else:\n",
    "    print('not greater')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "What did we do here?\n",
    "First, we used the `if` and `else` statements to determine what parts of the code to execute.\n",
    "Note that both lines containing `if` or `else` end with a `:` and the text beneath is indented.\n",
    "What do these tests do?\n",
    "The `if` test checks to see whether the variable value for `num` is greater than 100.\n",
    "If so, 'greater' would be written to the screen.\n",
    "Since 37 is smaller than 100, the code beneath the `else` is executed.\n",
    "The `else` statement code will run whenever the `if` test is false.\n",
    "\n",
    "### If, but not else\n",
    "\n",
    "The combination of `if` and `else` is very common, but both are not strictly required."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "source": [
    "num = 53\n",
    "if num > 100:\n",
    "    print('53 is greater than 100')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Note that here we use only the `if` statement, and because 53 is not greater than 100, nothing is printed to the screen.\n",
    "\n",
    "### The else-if case\n",
    "\n",
    "We can also have a second test for an `if` statment by using the `elif` (else-if) statement."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "num = -3\n",
    "if num > 0:\n",
    "    print(num, 'is positive')\n",
    "elif num == 0:\n",
    "    print(num, 'is zero')\n",
    "else:\n",
    "    print(num, 'is negative')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Makes sense, right?\n",
    "Note here that we use the `==` to test if a value is equal to another.\n",
    "The complete list of these comparison operators is given in the table below.\n",
    "\n",
    "| Operator   | Meaning                    |\n",
    "| ---------- | -------------------------- |\n",
    "| `<`        | Less than                  |\n",
    "| `<=`       | Less than or equal to      |\n",
    "| `==`       | Equal to                   |\n",
    "| `>=`       | Greater than or equal to   |\n",
    "| `>`        | Greater than               |\n",
    "| `!=`       | Not equal to               |\n",
    "\n",
    "### Multiple conditions\n",
    "\n",
    "We can also use `and` and `or` to have multiple conditions."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "if (1 > 0) and (-1 > 0):\n",
    "    print('Both parts are true')\n",
    "else:\n",
    "    print('One part is not true')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "if (1 < 0) or (-1 < 0):\n",
    "    print('At least one test is true')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This can be quite handy."
   ]
  }
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