sitc/python/1_2_Numbers_Strings.ipynb

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    "![](http://www.upm.es/sfs/Rectorado/Gabinete%20del%20Rector/Logos/UPM/EscPolitecnica/EscUpmPolit_p.gif \"UPM\")"
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   "source": [
    "# Course Notes for Learning Intelligent Systems"
   ]
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   "source": [
    "Department of Telematic Engineering Systems, Universidad Politécnica de Madrid, © Carlos A. Iglesias"
   ]
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   "metadata": {},
   "source": [
    "# Built-in Types: Booleans, Numbers and Strings"
   ]
  },
  {
   "cell_type": "markdown",
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   "source": [
    "Python comes with standard types that are built in the interpreter. \n",
    "\n",
    "The main built-in types are booleans, numeric, strings and sequences. More details can be found in the [Python documentation](https://docs.python.org/3/library/stdtypes.html)."
   ]
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   "source": [
    "## 1. Booleans"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "source": [
    "True and False # operations with booleans"
   ]
  },
  {
   "cell_type": "code",
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   "source": [
    "not True"
   ]
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   "source": [
    "True or False"
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   "source": [
    "## 2. Numbers"
   ]
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   "source": [
    "In Python3, there are the following [numeric types](https://docs.python.org/3/library/stdtypes.html#typesnumeric):\n",
    "* integers (int): 1, -1, ...\n",
    "* floating point numbers (float): 0.1, 1E2\n",
    "* complex numbers (complex): 2 + 3j\n",
    "Let's play a bit"
   ]
  },
  {
   "cell_type": "code",
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   "outputs": [],
   "source": [
    "2 + 2 # 2 plus 2 (integers)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "2.0 * 3.0 # 2.0 times 3.0 (floats)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "2.0 ** 4.0 # 2.0 to the power of 4 (float)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "(3 + 4j) + (5 + 5j) #add two complex numbers"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "10 / 3 # classic division"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "10 // 3 # floor division"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "10 % 3 # remainder"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "10e158*17e158 #overflow shown as 'inf', infinitive"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "type(10)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "type(2 + 3j)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "type(2.1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "type(2E3)"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 3. Strings"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Strings are **immutable sequences** of Unicode code points.\n",
    "\n",
    "Strings in Python can be enclosed in matching single quotes or double quotes."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"This is a string\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "'This is also a string'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"This is a string containing single quotes 'hi'\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "'This is string containing double quotes \"hi\"'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "'''This is \n",
    "\n",
    "a long string\n",
    "\n",
    "''' # Triple quoted strings are used for long strings that span several lines, \n",
    "    # We can use triple single quotes or triple double quotes for long strings"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Strings can contain special characters: \\n (new line), \\t (tab), \\a (beep) and \\\\\\ (slash character)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"String with special characters: \\n newline, \\a beep and \\\\ slash\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "\"concatenate \" + \"two strings\" #use of '+' for concatenating two strings"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "len('hola') # length of a string"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "type(\"hola\")"
   ]
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Strings are sequences, so they can be accessed through and index starting from 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s = \"hola\" # assign the string value \"hola\" to the variable s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s # get the value of s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[0]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[3]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s [-1] # we can start from the beginning (index 0, 1, 2, ...) or from the last position (-1, -2, ...)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Since Strings are sequences, they can be accessed with the *slice notation*: s[start:end]. The resulting slice includes the elements of the sequence from position start (included) to position end (excluded). Both arguments start and end are optional (default values: start->0, end->length)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[0:2] #slice [0,2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[:2] #slice [0,2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[:] #slice [0, len(s)]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[:-2]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s[-4:-2]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Since Python 1.4, you can use the extended slice notation: [start:end:step]. The slice moves from start before end is reached, and moves from one position to the next by step items.\n",
    "\n",
    "Step cannot be 0.\n",
    "\n",
    "If start or end are omitted, they become the end value (the end side depends on the sign of the step). This means, for a positive step, default start and end are [0,len), while for a negative step, the default values are [len, 0)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "se = \"This is a string\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "se[::1] # moves from 0 to len, and the index is incremented by 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "se[0:14:2] #take the even indexed characters from 0 to 14"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "se[::-1] #reverse the string"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "se[:4:-1]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can use also operations (+, *) with strings"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = 'b'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "se + \" plus \" + se + \" plus \"+ a*3"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can also used methods for Strings, such as lower(), upper(), split(), ...\n",
    "\n",
    "You can check the available methods by writing a String variable, \".\", and pressing Tab."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s.lower()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s.upper()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "s.split('o') # splits String "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Exercises"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Think if the following expressions are ok, and which will be the result.\n",
    "\n",
    "Execute the cells and check your answers."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "\"hohoho\".split('h')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "type(\"hohoho\".split('h'))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Licence"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The notebook is freely licensed under under the [Creative Commons Attribution Share-Alike license](https://creativecommons.org/licenses/by/2.0/).  \n",
    "\n",
    "© Carlos A. Iglesias, Universidad Politécnica de Madrid."
   ]
  }
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