Just review of python basic

PythonBaiscsCheatsheet.ipynb

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   "cell_type": "markdown",
   "metadata": {
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   "source": [
    "## Variables, statements"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
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    "slideshow": {
     "slide_type": "fragment"
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "47\n"
     ]
    }
   ],
   "source": [
    "var1 = 42\n",
    "var1 += var1 * 12 / 100  # in python3 will be float\n",
    "print var1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'var1' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-2-2ebe64d58721>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;32mdel\u001b[0m \u001b[0mvar1\u001b[0m\u001b[0;34m;\u001b[0m \u001b[0;32mprint\u001b[0m \u001b[0mvar1\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mNameError\u001b[0m: name 'var1' is not defined"
     ]
    }
   ],
   "source": [
    "del var1; print var1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Builtin data types / collections"
   ]
  },
  {
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   "execution_count": 3,
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    {
     "data": {
      "text/plain": [
       "(int,\n",
       " float,\n",
       " complex,\n",
       " str,\n",
       " unicode,\n",
       " 'Escaped \"string\"',\n",
       " 'Raw \\\\\"string\\\\\"',\n",
       " 'single quotes',\n",
       " 'tripple quotes',\n",
       " 'triple single quotes',\n",
       " 16,\n",
       " 8,\n",
       " 2)"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "(type(2), type(3.), type(3+1j), type(\"String\"), type(u\"Unicode string\"),\n",
    "  \"Escaped \\\"string\\\"\", r\"Raw \\\"string\\\"\",  # escapes\n",
    " 'single quotes', \"\"\"tripple quotes\"\"\", '''triple single quotes''',\n",
    "  0x10, 0o10, 0b10  # numbers\n",
    ")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
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   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'loc': {'x': 1, 'y': 2},\n",
       " 'people': [('John', 35), ('Henry', 40)],\n",
       " 'tags': {'it', 'python'}}"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "{\"people\": [(\"John\", 35), (\"Henry\", 40)],  # list of tuples\n",
    " \"loc\": {\"x\":1, \"y\":2},  # dict\n",
    " \"tags\": {\"it\", \"python\"}  # set\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### List operations"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 2, 3, 4]\n",
      "[1, 'a', 'b', 'c', 4]\n",
      "[1, 'a', 'b', 'c']\n"
     ]
    }
   ],
   "source": [
    "list1 = [1, 2, 3]\n",
    "list1.append(4); print list1\n",
    "list1[1:3] = \"abc\"; print list1\n",
    "print list1[:-1]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1, 'a', 'b', 'c', 4, 0, 2, 4, 6, 8]\n"
     ]
    }
   ],
   "source": [
    "list1.extend(range(0, 10, 2)); print list1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['Begin', 1, 'a', 'b', 'c', 4, 0, 2, 4, 6, 8, '-', '-']\n"
     ]
    }
   ],
   "source": [
    "print [\"Begin\"] + list1 + [\"-\"]*2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0, 1, 2, 4, 4, 6, 8, 'a', 'b', 'c']\n"
     ]
    }
   ],
   "source": [
    "list1.sort(); print list1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### Dictionary operations"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
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   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'a': 2, 'c': 4, 'b': 2}\n",
      "2\n"
     ]
    }
   ],
   "source": [
    "dict1 = {'a': 1, 'b': 2}\n",
    "dict1['a'] = 2; dict1.setdefault('b', 3); dict1.setdefault('c', 4)\n",
    "print dict1\n",
    "print dict1['a']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "'d'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-10-031bb2effc7f>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0;32mprint\u001b[0m \u001b[0mdict1\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m'd'\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m: 'd'"
     ]
    }
   ],
   "source": [
    "print dict1['d']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
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   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "(None, 2)"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "dict1.get('d'), dict1.get('a')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Control-flow"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'a': 2, 'c': 4, 'b': 2}\n"
     ]
    }
   ],
   "source": [
    "if dict1: print dict1\n",
    "else:\n",
    "    print \"empty dict1\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "|    0 | 0          |\n",
      "|    1 | 1          |\n",
      "|    2 | 2          |\n",
      "|    3 | 4          |\n",
      "|    4 | 4          |\n",
      "|    5 | 6          |\n",
      "|    6 | 8          |\n",
      "|    7 | 'a'        |\n",
      "|    8 | 'b'        |\n",
      "|    9 | 'c'        |\n"
     ]
    }
   ],
   "source": [
    "for i, x in enumerate(list1):\n",
    "    print \"| %4d | %-10r |\" % (i, x)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3\n",
      "9\n"
     ]
    }
   ],
   "source": [
    "i = 0\n",
    "while i < 10:\n",
    "    i += 3\n",
    "    if (i % 2) == 0: continue\n",
    "    print i"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Functions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "120"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def fact(n):\n",
    "    return 1 if n == 0 else n * fact(n-1)\n",
    "fact(5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[1, 1, 2, 3, 5, 8, 13, 21, 34, 55]"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def fib(n, init=(1, 1)):\n",
    "    if n < 2: return init[n]\n",
    "    else: return fib(n-1, init=(init[1], sum(init)))\n",
    "[fib(k) for k in range(10)]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### Keyword global"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "ename": "UnboundLocalError",
     "evalue": "local variable 'last_id' referenced before assignment",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mUnboundLocalError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[0;32m<ipython-input-29-44cd0a45576c>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      3\u001b[0m     \u001b[0mlast_id\u001b[0m \u001b[0;34m+=\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m     \u001b[0;32mreturn\u001b[0m \u001b[0mlast_id\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 5\u001b[0;31m \u001b[0mget_id\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[0;32m<ipython-input-29-44cd0a45576c>\u001b[0m in \u001b[0;36mget_id\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0mlast_id\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;36m0\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      2\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0mget_id\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 3\u001b[0;31m     \u001b[0mlast_id\u001b[0m \u001b[0;34m+=\u001b[0m \u001b[0;36m1\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      4\u001b[0m     \u001b[0;32mreturn\u001b[0m \u001b[0mlast_id\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0mget_id\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
      "\u001b[0;31mUnboundLocalError\u001b[0m: local variable 'last_id' referenced before assignment"
     ]
    }
   ],
   "source": [
    "last_id = 0\n",
    "def get_id():\n",
    "    last_id += 1\n",
    "    return last_id\n",
    "get_id()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[1, 2, 3, 4, 5]"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def get_id():\n",
    "    global last_id\n",
    "    last_id += 1\n",
    "    return last_id\n",
    "[get_id() for k in range(5)]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## I/O\n",
    "```python\n",
    "def store(filepath, text):\n",
    "    \"\"\"Store text to file\n",
    "    \n",
    "    filepath path to file\n",
    "    text: content to store\n",
    "    \n",
    "    returns amount of actual bytes written to the file\"\"\"\n",
    "    with open(filepath, \"w\") as fp:\n",
    "        fp.write(text)\n",
    "        return fp.tell()\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "source": [
    "```python\n",
    "def chunked_read(filepath, chunk_size=4096):\n",
    "    \"\"\"Generate stream of chunks read from file\"\"\"\n",
    "    with open(filepath, \"rb\") as fp:\n",
    "        while True:\n",
    "            chunk = fp.read(chunk_size)\n",
    "            if len(chunk) == 0: break  # end of file\n",
    "            yield chunk\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "subslide"
    }
   },
   "source": [
    "### Filesystem example\n",
    "```python\n",
    "import os, os.path\n",
    "for entry in os.listdir('.'):\n",
    "    if os.path.isdir(entry): t = 'd'\n",
    "    elif os.path.islink(entry): t = 'l'\n",
    "    else: t = '-'\n",
    "    print '%c %s' % (t, entry)\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "slideshow": {
     "slide_type": "slide"
    }
   },
   "source": [
    "## Exceptions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "No such key 'abc'\n",
      "Do this regardless of exceptions/returns/breaks\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    dict1['abc']\n",
    "except KeyError as e:\n",
    "    print \"No such key %r\" % (e.args[0],)\n",
    "finally:\n",
    "    print \"Do this regardless of exceptions/returns/breaks\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 39,
   "metadata": {
    "collapsed": false,
    "slideshow": {
     "slide_type": "fragment"
    }
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hi\n",
      "there\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    print \"Hi\"\n",
    "except: pass\n",
    "else:\n",
    "    print \"there\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
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