cds-104_Datenbanken/Block-2/Python_Wiederholung_mit_Code.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Python - Kurzwiederholung\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Elementare Datentypen"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# eine Variable mit einem int-Wert\n",
    "i = 10\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Python kann sher grosse Zahlen verarbeiten:\n",
    "j = 123456395823842193412376429384\n",
    "j+1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# int-Zahlen sind richtige Objekte - sie brauchen mehr Speicher, \n",
    "# haben aber auch mehr Fähigkeiten als in anderen Sprachen\n",
    "import sys\n",
    "\n",
    "print(sys.getsizeof(10)) # Specherverbrauch einer einzelnen Zahl\n",
    "print(i.bit_length())    # Methoden, hier Bitlänge der Zahl"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# ein Float \n",
    "f = 5.0\n",
    "\n",
    "# auch Floats haben Methoden\n",
    "print(f.is_integer())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Floats haben so ihre Probleme...\n",
    "0.1 + 0.2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Strings, Konkatenation\n",
    "s = \"Hello\" + \" \" + \"World\"\n",
    "s"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Boolsche Werte\n",
    "a = True\n",
    "b = False\n",
    "\n",
    "print(a and b)\n",
    "print(a or b)\n",
    "type(a)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Umwandlung von Datentypen"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# zahl in string umwandeln\n",
    "i = 5\n",
    "str(i)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# string in zahl umwandeln\n",
    "s = \"55\"\n",
    "float(s)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Kontrollstrukturen: if, while, for, range-Funktion"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "i = 10\n",
    "\n",
    "if i > 5:\n",
    "    print(\"i ist grösser 5\")\n",
    "    \n",
    "while i > 0:\n",
    "    print(i)\n",
    "    i = i - 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "for i in range(5):\n",
    "    print(i)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# rückwärts zählen\n",
    "for i in range(10, 4, -1):\n",
    "    print(i)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Beispiele für Funktionen"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def add(i, j):\n",
    "    return i+j"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "print(add(2, 3))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Listen, Indizierung, Slicing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Platznummern\n",
    "#    0  1  2  3  4  5  6\n",
    "l = [1, 2, 3, 4, 5, 6, 7]\n",
    "\n",
    "# slicing\n",
    "l[1::2]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# enumerate: Aufzählen einer Liste (Tupelbildung mit Index)\n",
    "list(enumerate([5,9,42]))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "l = [\"test\", 1, 5.5, True] # Listen können gemischte Werte enthalten"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Tupel"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "t = (4, 5)  # Tupel einpacken\n",
    "a, b = t    # Tupel auspacken\n",
    "\n",
    "print(a)\n",
    "print(b)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "builtin-Funktionen, Standardbibliothek"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# builtin-Funktion\n",
    "# range, list, int, float, len, sum, bool, tuple "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# ein Import - hier math\n",
    "import math"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "math.exp(2.0)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Dictionaries"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "d = { 'eins': 'one', 'zwei': 'two' }\n",
    "\n",
    "d.keys(), d.values()\n",
    "\n",
    "for key, value in d.items():\n",
    "    print(key, '->', value)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "List-Comprehensions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Quadratzahlen mit gerader Basis\n",
    "[ x*x for x in range(0,21) if x % 2 == 0 ]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Statistics"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = [3,4,5,6,7]\n",
    "mean(a), variance(a)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "b = [0, 2, 4, 6, 8, 10]\n",
    "mean(b), variance(b)"
   ]
  }
 ],
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