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Advanced Python TrainingDecember 13-14, 2013Global Analytics -- http://nbviewer.ipython.org/gist/anandology/7939444
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day1.ipynb
{
"metadata": {
"name": ""
},
"nbformat": 3,
"nbformat_minor": 0,
"worksheets": [
{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Advanced Python Training - Day 1\n",
"December 13-14, 2013<br/>\n",
"Global Analytics"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def f(a, x=[]):\n",
" x.append(a)\n",
" return x\n"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 1
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f(0, [1, 2])"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 2,
"text": [
"[1, 2, 0]"
]
}
],
"prompt_number": 2
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f(1)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 3,
"text": [
"[1]"
]
}
],
"prompt_number": 3
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f(2)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 4,
"text": [
"[1, 2]"
]
}
],
"prompt_number": 4
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Functions in detail**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def square(x):\n",
" return x*x\n",
"\n",
"print square(4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"16\n"
]
}
],
"prompt_number": 5
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f = square"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 6
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 7,
"text": [
"<function __main__.square>"
]
}
],
"prompt_number": 7
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f(4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 8,
"text": [
"16"
]
}
],
"prompt_number": 8
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def sum_of_squares(x, y):\n",
" return square(x) + square(y)\n",
"\n",
"print sum_of_squares(3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"25\n"
]
}
],
"prompt_number": 9
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def cube(x): return x*x*x\n",
"\n",
"def sum_of_cubes(x, y):\n",
" return cube(x) + cube(y)\n",
"\n",
"print sum_of_cubes(3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"91\n"
]
}
],
"prompt_number": 10
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def sumof(f, x, y):\n",
" return f(x) + f(y)\n",
"\n",
"print sumof(square, 3, 4)\n",
"print sumof(cube, 3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"25\n",
"91\n"
]
}
],
"prompt_number": 11
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"names = [\"C\", \"c++\", \"Python\", \"perl\", \"Haskell\", \"java\"]\n",
"sorted(names)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 13,
"text": [
"['C', 'Haskell', 'Python', 'c++', 'java', 'perl']"
]
}
],
"prompt_number": 13
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"sorted(names, key=len)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 14,
"text": [
"['C', 'c++', 'perl', 'java', 'Python', 'Haskell']"
]
}
],
"prompt_number": 14
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a function `isorted` to sort given names without considering the case.\n",
"\n",
" >>> isorted([\"C\", \"Python\", \"c++\", \"java\", \"Haskell\"])\n",
" [\"C\", \"c++\", \"Haskell\", \"java\", \"Python\"]"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def lower(s):\n",
" return s.lower()\n",
"\n",
"def isorted(values):\n",
" #return sorted(values, key=lower)\n",
" return sorted(values, key=lambda s: s.lower())\n",
"\n",
"isorted([\"C\", \"Python\", \"c++\", \"java\", \"Haskell\"])\n",
" "
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 17,
"text": [
"['C', 'c++', 'Haskell', 'java', 'Python']"
]
}
],
"prompt_number": 17
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"min(names)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 18,
"text": [
"'C'"
]
}
],
"prompt_number": 18
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"max(names)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 19,
"text": [
"'perl'"
]
}
],
"prompt_number": 19
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"max(names, key=len)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 20,
"text": [
"'Haskell'"
]
}
],
"prompt_number": 20
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a function `maximum` that works like built-in `max` function. It should take an optional keyword argument `key`, when supplied should use `key(x)` and `key(y)` for comparing values `x` and `y`.\n",
"\n",
" >>> maximum([\"Python\", \"Haskell\"])\n",
" 'Python'\n",
" >>> maximum([\"Python\", \"Haskell\"], key=len)\n",
" 'Haskell'"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def maximum(values, key=None):\n",
" if key is None:\n",
" key = lambda x:x\n",
" max = values[0]\n",
" for v in values:\n",
" if key(v) > key(max):\n",
" max = v\n",
" return max\n",
"\n"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 21
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Example: json_encode**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"import json\n",
"print json.dumps({\"x\": 1, \"y\": [2, 3, \"hello\", {\"z\": 4}], \"a\": True})"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"{\"y\": [2, 3, \"hello\", {\"z\": 4}], \"x\": 1, \"a\": true}\n"
]
}
],
"prompt_number": 23
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def json_encode(data):\n",
" if isinstance(data, str):\n",
" return '\"' + data + '\"'\n",
" elif isinstance(data, int):\n",
" return str(data)\n",
" elif isinstance(data, list):\n",
" x = [json_encode(d) for d in data]\n",
" return \"[\" + \", \".join(x) + \"]\"\n",
" \n",
"print json_encode(1)\n",
"print json_encode(\"hello\")\n",
"print json_encode([1, 2, \"hello\", [\"foo\", \"bar\", 3]])"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1\n",
"\"hello\"\n",
"[1, 2, \"hello\", [\"foo\", \"bar\", 3]]\n"
]
}
],
"prompt_number": 29
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Closures - Inner Functions**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def make_adder(x):\n",
" def adder(y):\n",
" return x + y\n",
" return adder\n",
"\n",
"add5 = make_adder(5)\n",
"print add5(3)\n",
"\n",
"add4 = make_adder(4)\n",
"print add4(3)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"8\n",
"7\n"
]
}
],
"prompt_number": 30
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\"hello\".center(40)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 34,
"text": [
"' hello '"
]
}
],
"prompt_number": 34
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a function make_centeralign, that takes width as argument and returns a new function that takes a string as argument and center align that.\n",
"\n",
" >>> center20 = make_centeralign(20)\n",
" >>> center20('helloworld')\n",
" ' helloworld '"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Functions with variable number of arguments**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"max(1, 2, 3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 36,
"text": [
"4"
]
}
],
"prompt_number": 36
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"**Problem** write a function `add` that takes variable number of arguments and computes their sum.\n",
"\n",
" >>> add(1, 2, 3, 4)\n",
" 10\n",
" >>> add(1, 2, 3)\n",
" 6"
],
"language": "python",
"metadata": {},
"outputs": []
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def add(*args):\n",
" print \"args =\", args\n",
" return sum(args)\n",
"\n",
"print add(1, 2, 3, 4)\n",
"print add(1, 2, 3)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"args = (1, 2, 3, 4)\n",
"10\n",
"args = (1, 2, 3)\n",
"6\n"
]
}
],
"prompt_number": 38
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def log(level, *args):\n",
" message = \" \".join([str(a) for a in args])\n",
" print \"[%s] %s\" % (level, message)\n",
" \n",
"log(\"INFO\", \"hello world\")\n",
"log(\"DEBUG\", \"square\", 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[INFO] hello world\n",
"[DEBUG] square 4\n"
]
}
],
"prompt_number": 40
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def info(*args):\n",
" log(\"INFO\", *args)\n",
" \n",
"info(\"hello\", \"world\")"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[INFO] hello world\n"
]
}
],
"prompt_number": 41
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def add(x, y):\n",
" return x + y"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 42
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"func = add\n",
"args = [2, 3]\n",
"print func(*args)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"5\n"
]
}
],
"prompt_number": 43
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"max(3, 4, *args)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 44,
"text": [
"4"
]
}
],
"prompt_number": 44
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def diff(x, y):\n",
" return x - y\n",
"\n",
"print diff(5, 3)\n",
"print diff(5, y=3)\n",
"print diff(x=5, y=3)\n",
"print diff(y=3, x=5)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2\n",
"2\n",
"2\n",
"2\n"
]
}
],
"prompt_number": 45
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def mydict(**foo):\n",
" return foo\n",
"\n",
"print mydict(a=1, b=2)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"{'a': 1, 'b': 2}\n"
]
}
],
"prompt_number": 46
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def render_template(name, **kwargs):\n",
" print \"rendering template %s using %s\" % (name, kwargs)"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 47
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"render_template(\"a.html\", x=1, y=2)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"rendering template a.html using {'y': 2, 'x': 1}\n"
]
}
],
"prompt_number": 48
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Decorators"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def square(x):\n",
" print \"square\", x\n",
" value = x*x\n",
" print value\n",
" return value\n",
"\n",
"def sum_of_squares(x, y):\n",
" print \"sum_of_squares\", x, y\n",
" return square(x) + square(y)\n",
"\n",
"print sum_of_squares(3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"sum_of_squares 3 4\n",
"square 3\n",
"9\n",
"square 4\n",
"16\n",
"25\n"
]
}
],
"prompt_number": 52
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file trace1.py\n",
"import os\n",
"\n",
"level = 0\n",
"\n",
"def log(*args):\n",
" if os.getenv(\"DEBUG\"):\n",
" print \" \".join([str(a) for a in args])\n",
"\n",
"def trace(f):\n",
" def g(*args):\n",
" global level\n",
" log(\"| \" * level + \"|--\", f.__name__, args)\n",
" level += 1 \n",
" value = f(*args)\n",
" level -= 1 \n",
" log(\"| \" * level + \"|--\", \"returned\", value)\n",
" return value\n",
" return g"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting trace1.py\n"
]
}
],
"prompt_number": 87
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file sumofsquares.py\n",
"from trace1 import trace\n",
"\n",
"@trace\n",
"def square(x):\n",
" return x*x\n",
"\n",
"@trace\n",
"def sum_of_squares(x, y):\n",
" return square(x) + square(y)\n",
"\n",
"#square = trace(square)\n",
"#sum_of_squares = trace(sum_of_squares)\n",
"\n",
"print sum_of_squares(3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting sumofsquares.py\n"
]
}
],
"prompt_number": 93
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!DEBUG=true python sumofsquares.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"|-- sum_of_squares (3, 4)\r\n",
"| |-- square (3,)\r\n",
"| |-- returned 9\r\n",
"| |-- square (4,)\r\n",
"| |-- returned 16\r\n",
"|-- returned 25\r\n",
"25\r\n"
]
}
],
"prompt_number": 96
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file fib1.py\n",
"\n",
"from trace1 import trace\n",
"\n",
"def fib(n):\n",
" if n == 0 or n == 1:\n",
" return 1\n",
" else:\n",
" return fib(n-1) + fib(n-2)\n",
" \n",
"fib = trace(fib)\n",
"print fib(4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting fib1.py\n"
]
}
],
"prompt_number": 95
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!DEBUG=true python fib1.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"|-- fib (4,)\r\n",
"| |-- fib (3,)\r\n",
"| | |-- fib (2,)\r\n",
"| | | |-- fib (1,)\r\n",
"| | | |-- returned 1\r\n",
"| | | |-- fib (0,)\r\n",
"| | | |-- returned 1\r\n",
"| | |-- returned 2\r\n",
"| | |-- fib (1,)\r\n",
"| | |-- returned 1\r\n",
"| |-- returned 3\r\n",
"| |-- fib (2,)\r\n",
"| | |-- fib (1,)\r\n",
"| | |-- returned 1\r\n",
"| | |-- fib (0,)\r\n",
"| | |-- returned 1\r\n",
"| |-- returned 2\r\n",
"|-- returned 5\r\n",
"5\r\n"
]
}
],
"prompt_number": 92
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a decorator function `logtime` to print the amount of time a function is taken to execute.\n",
"\n",
" @logtime\n",
" def timepass(n):\n",
" result = 0\n",
" for i in range(n):\n",
" for j in range(i):\n",
" result += i*j\n",
" return result \n",
" \n",
" print timepass(100)\n",
" # timepass(100) took 0.01 seconds"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"import time\n",
"t1 = time.time()\n",
"for i in range(1000000): \n",
" pass\n",
"t2 = time.time()\n",
"print t2-t1"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"0.115938901901\n"
]
}
],
"prompt_number": 97
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file logtime.py\n",
"import time\n",
"\n",
"def logtime(f):\n",
" def g(*args):\n",
" t1 = time.time()\n",
" result = f(*args)\n",
" t2 = time.time()\n",
" print \"%s%s took %.3f seconds\" % (f.__name__, args, t2-t1)\n",
" return result\n",
" return g\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting logtime.py\n"
]
}
],
"prompt_number": 104
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file fib0.py\n",
"\n",
"from trace1 import trace\n",
"\n",
"@trace\n",
"def fib(n):\n",
" if n == 0 or n == 1:\n",
" return 1\n",
" else:\n",
" return fib(n-1) + fib(n-2)\n",
"\n",
"if __name__ == \"__main__\": \n",
" import sys\n",
" fib(int(sys.argv[1]))"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting fib0.py\n"
]
}
],
"prompt_number": 131
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!DEBUG=1 time python fib0.py 5"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"|-- fib (5,)\r\n",
"| |-- fib (4,)\r\n",
"| | |-- fib (3,)\r\n",
"| | | |-- fib (2,)\r\n",
"| | | | |-- fib (1,)\r\n",
"| | | | |-- returned 1\r\n",
"| | | | |-- fib (0,)\r\n",
"| | | | |-- returned 1\r\n",
"| | | |-- returned 2\r\n",
"| | | |-- fib (1,)\r\n",
"| | | |-- returned 1\r\n",
"| | |-- returned 3\r\n",
"| | |-- fib (2,)\r\n",
"| | | |-- fib (1,)\r\n",
"| | | |-- returned 1\r\n",
"| | | |-- fib (0,)\r\n",
"| | | |-- returned 1\r\n",
"| | |-- returned 2\r\n",
"| |-- returned 5\r\n",
"| |-- fib (3,)\r\n",
"| | |-- fib (2,)\r\n",
"| | | |-- fib (1,)\r\n",
"| | | |-- returned 1\r\n",
"| | | |-- fib (0,)\r\n",
"| | | |-- returned 1\r\n",
"| | |-- returned 2\r\n",
"| | |-- fib (1,)\r\n",
"| | |-- returned 1\r\n",
"| |-- returned 3\r\n",
"|-- returned 8\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
" 0.01 real 0.01 user 0.00 sys\r\n"
]
}
],
"prompt_number": 135
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file memoize.py\n",
"\n",
"def memoize(f):\n",
" cache = {}\n",
" def g(*args):\n",
" if args not in cache:\n",
" cache[args] = f(*args)\n",
" return cache[args]\n",
" return g\n",
"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing memoize.py\n"
]
}
],
"prompt_number": 120
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file fib2.py\n",
"\n",
"from trace1 import trace\n",
"from memoize import memoize\n",
"\n",
"@memoize\n",
"@trace\n",
"def fib(n):\n",
" if n == 0 or n == 1:\n",
" return 1\n",
" else:\n",
" return fib(n-1) + fib(n-2)\n",
"\n",
"if __name__ == \"__main__\": \n",
" import sys\n",
" fib(int(sys.argv[1]))"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting fib2.py\n"
]
}
],
"prompt_number": 128
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!DEBUG=1 python fib2.py 5"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"|-- fib (5,)\r\n",
"| |-- fib (4,)\r\n",
"| | |-- fib (3,)\r\n",
"| | | |-- fib (2,)\r\n",
"| | | | |-- fib (1,)\r\n",
"| | | | |-- returned 1\r\n",
"| | | | |-- fib (0,)\r\n",
"| | | | |-- returned 1\r\n",
"| | | |-- returned 2\r\n",
"| | |-- returned 3\r\n",
"| |-- returned 5\r\n",
"|-- returned 8\r\n"
]
}
],
"prompt_number": 139
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** write a decorator function `with_retries` that retries the function 5 times before giving up.\n",
"\n",
" @with_retries\n",
" def wget(url):\n",
" return urllib2.urlopen(url).read()\n",
" \n",
" wget(\"http://google.com/no-such-page\")\n",
" \n",
"should print something like:\n",
"\n",
" Error Not Found, retrying (1)...\n",
" Error Not Found, retrying (2)...\n",
" Error Not Found, retrying (3)...\n",
" Error Not Found, retrying (4)...\n",
" Error Not Found, retrying (5)...\n",
" Giving up."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"How about passing the number of attempts as argument to `with_retries`? May be another optional `sleeptime` between retries? \n",
"\n",
" @with_retries(attempts=5, sleeptime=5)\n",
" def wget(url):\n",
" return urllib2.urlopen(url).read()\n"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Lets look at expressions in Python a bit.\n",
"\n",
" (1 + 2) * 3 \n",
"1+2 is evaluated and added to 3\n",
" \n",
" f(x) + 3 \n",
"f(x) is evaluated and added to 3\n",
" \n",
" f(g(x)) \n",
"g(x) is evaulated first and the value is passed to f\n",
"\n",
"It is same as:\n",
" \n",
" tmp = g(x)\n",
" f(tmp)\n",
" \n",
"Similarly\n",
"\n",
" @foo(x)\n",
" def f():\n",
" ...\n",
"is same as:\n",
"\n",
" decor = foo(x)\n",
" @decor\n",
" def f():\n",
" ...\n",
" \n",
"Which is same as:\n",
"\n",
" decor = foo(x)\n",
" def f():\n",
" ...\n",
" f = decor(f)"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file retries.py\n",
"import urllib2\n",
"import time\n",
"\n",
"def with_retries(attempts=5, sleeptime=0):\n",
" def decorator(f):\n",
" def g(*args):\n",
" for i in range(attempts):\n",
" try:\n",
" return f(*args)\n",
" except Exception, e:\n",
" print \"Error %s, retrying... (%d)\" % (e, i+1) \n",
" if sleeptime:\n",
" time.sleep(sleeptime)\n",
" print \"Giving up.\"\n",
" return g\n",
" return decorator\n",
"\n",
"@with_retries(attempts=5, sleeptime=0.1)\n",
"def wget(url):\n",
" return urllib2.urlopen(url).read()\n",
"\n",
"if __name__ == \"__main__\":\n",
" wget(\"http://google.com/no-such-page\")\n",
" "
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting retries.py\n"
]
}
],
"prompt_number": 144
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python retries.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (1)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (2)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (3)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (4)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (5)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Giving up.\r\n"
]
}
],
"prompt_number": 145
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"A trick to make it look simpler."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file retries2.py\n",
"import urllib2\n",
"import time\n",
"\n",
"def with_retries(f=None, attempts=5, sleeptime=0):\n",
" print \"with_retries\", f, attempts, sleeptime\n",
" if f is None:\n",
" return lambda f: with_retries(f, attempts, sleeptime)\n",
"\n",
" print \"defining g\" \n",
" def g(*args):\n",
" for i in range(attempts):\n",
" try:\n",
" return f(*args)\n",
" except Exception, e:\n",
" print \"Error %s, retrying... (%d)\" % (e, i+1) \n",
" if sleeptime:\n",
" time.sleep(sleeptime)\n",
" print \"Giving up.\"\n",
" return g\n",
"\n",
"@with_retries(attempts=5, sleeptime=0.1)\n",
"def wget(url):\n",
" return urllib2.urlopen(url).read()\n",
"\n",
"if __name__ == \"__main__\":\n",
" wget(\"http://google.com/no-such-page\")\n",
" "
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing retries2.py\n"
]
}
],
"prompt_number": 146
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python retries2.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"with_retries None 5 0.1\r\n",
"with_retries <function wget at 0x1005d8b18> 5 0.1\r\n",
"defining g\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (1)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (2)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (3)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (4)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Error HTTP Error 404: Not Found, retrying... (5)\r\n"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Giving up.\r\n"
]
}
],
"prompt_number": 147
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a decorator `ignore_exception` that takes exception type as argument and ignores if that exception is raised by the function being decorated. (The new function should return `None` in case of exception).\n",
"\n",
" @ignore_exception(IOError)\n",
" def readfile(filename):\n",
" return open(filename).read()\n",
" "
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Minor issues**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def debug(f):\n",
" def g(*a):\n",
" print f.__name__, a\n",
" return f(*a)\n",
" return g\n",
"\n",
"def square1(x):\n",
" \"\"\"Computes square of a number.\"\"\"\n",
" return x*x\n",
"\n",
"@debug\n",
"def square2(x):\n",
" \"\"\"Computes square of a number.\"\"\"\n",
" return x*x\n",
"\n",
"print square1\n",
"print square2"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"<function square1 at 0x1023a3140>\n",
"<function g at 0x103f1a578>\n"
]
}
],
"prompt_number": 148
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"help(square1)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Help on function square1 in module __main__:\n",
"\n",
"square1(x)\n",
" Computes square of a number.\n",
"\n"
]
}
],
"prompt_number": 149
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"help(square2)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Help on function g in module __main__:\n",
"\n",
"g(*a)\n",
"\n"
]
}
],
"prompt_number": 150
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"The `functools.wraps` functions fixes that."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"import functools\n",
"\n",
"def debug(f):\n",
" @functools.wraps(f)\n",
" def g(*a):\n",
" print f.__name__, a\n",
" return f(*a)\n",
" return g\n",
"\n",
"\n",
"@debug\n",
"def square3(x):\n",
" \"\"\"Computes square of a number.\"\"\"\n",
" return x*x\n",
"\n",
"print square1\n",
"print square2\n",
"print square3\n",
"help(square3)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"<function square1 at 0x1023a3140>\n",
"<function g at 0x103f1a578>\n",
"<function square3 at 0x103f1a758>\n",
"Help on function square3 in module __main__:\n",
"\n",
"square3(*a)\n",
" Computes square of a number.\n",
"\n"
]
}
],
"prompt_number": 155
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Classes"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"class Foo:\n",
" x = 1\n",
"\n",
"f1 = Foo()\n",
"f2 = Foo()\n",
"print Foo.x, f1.x, f2.x"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1 1 1\n"
]
}
],
"prompt_number": 156
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"f2.x = 2\n",
"print Foo.x, f1.x, f2.x"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1 1 2\n"
]
}
],
"prompt_number": 157
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"Foo.x = 3\n",
"print Foo.x, f1.x, f2.x"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"3 3 2\n"
]
}
],
"prompt_number": 158
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"How does Python stores default values for functions?"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def incr(x, amount=1):\n",
" return x+amount"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 159
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 160,
"text": [
"<function __main__.incr>"
]
}
],
"prompt_number": 160
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"dir(incr)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 161,
"text": [
"['__call__',\n",
" '__class__',\n",
" '__closure__',\n",
" '__code__',\n",
" '__defaults__',\n",
" '__delattr__',\n",
" '__dict__',\n",
" '__doc__',\n",
" '__format__',\n",
" '__get__',\n",
" '__getattribute__',\n",
" '__globals__',\n",
" '__hash__',\n",
" '__init__',\n",
" '__module__',\n",
" '__name__',\n",
" '__new__',\n",
" '__reduce__',\n",
" '__reduce_ex__',\n",
" '__repr__',\n",
" '__setattr__',\n",
" '__sizeof__',\n",
" '__str__',\n",
" '__subclasshook__',\n",
" 'func_closure',\n",
" 'func_code',\n",
" 'func_defaults',\n",
" 'func_dict',\n",
" 'func_doc',\n",
" 'func_globals',\n",
" 'func_name']"
]
}
],
"prompt_number": 161
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr.__defaults__"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 162,
"text": [
"(1,)"
]
}
],
"prompt_number": 162
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr.__defaults__ = (5,)"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 163
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr(4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 164,
"text": [
"9"
]
}
],
"prompt_number": 164
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr.__name__"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 165,
"text": [
"'incr'"
]
}
],
"prompt_number": 165
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr.__name__ = \"not_incr\""
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 166
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"incr"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 167,
"text": [
"<function __main__.not_incr>"
]
}
],
"prompt_number": 167
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file numbers.txt\n",
"1 one\n",
"2 two\n",
"3 three\n",
"4 four\n",
"5 five\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting numbers.txt\n"
]
}
],
"prompt_number": 170
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def wordcount(fileobj):\n",
" lc = len(fileobj.readlines())\n",
" fileobj.seek(0)\n",
" wc = len(fileobj.read().split())\n",
" fileobj.seek(0) \n",
" cc = len(fileobj.read())\n",
" print lc, wc, cc\n",
" \n",
"print wordcount(open('numbers.txt'))"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"5 10 33\n",
"None\n"
]
}
],
"prompt_number": 172
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"class FakeFile:\n",
" def __init__(self, lines):\n",
" self.lines = lines\n",
" \n",
" def readlines(self):\n",
" return self.lines\n",
" \n",
" def read(self):\n",
" return \"\".join(self.lines)\n",
" \n",
" def seek(self, pos):\n",
" pass\n",
" \n",
"ff = FakeFile([\"one\\n\", \"two\\n\", \"three\\n\", \"four \\n\"]) \n",
" "
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 173
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"wordcount(ff)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"4 4 20\n"
]
}
],
"prompt_number": 174
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a class UpperCaseFile that takes a file object as argument and behaves like a file, but returns all the contents in uppercase.\n",
"\n",
" f = UpperCaseFile(open(\"numbers.txt\"))\n",
" f.readline() # should return \"1 ONE\\n\""
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Special class methods**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"class Point:\n",
" def __init__(self, x, y):\n",
" self.x = x\n",
" self.y = y\n",
" \n",
" def __str__(self):\n",
" return \"(%s, %s)\" % (self.x, self.y)"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 178
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"p1 = Point(1, 2)\n",
"p2 = Point(3, 4)"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 179
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print p1"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(1, 2)\n"
]
}
],
"prompt_number": 180
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print [p1, p2]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[<__main__.Point instance at 0x103f3f320>, <__main__.Point instance at 0x103f3f200>]\n"
]
}
],
"prompt_number": 181
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print [1, \"1\"]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[1, '1']\n"
]
}
],
"prompt_number": 182
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print str(1)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1\n"
]
}
],
"prompt_number": 183
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print str('1')"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1\n"
]
}
],
"prompt_number": 184
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print repr(1), repr('1')"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1 '1'\n"
]
}
],
"prompt_number": 185
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"class Point2:\n",
" def __init__(self, x, y):\n",
" self.x = x\n",
" self.y = y\n",
" \n",
" def __str__(self):\n",
" return \"(%s, %s)\" % (self.x, self.y)\n",
" \n",
" def __repr__(self):\n",
" return \"Point(%s, %s)\" % (self.x, self.y)\n",
" \n",
"p1 = Point2(1, 2)\n",
"p2 = Point2(3, 4)\n",
"print p1, p2\n",
"print [p1, p2]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(1, 2) (3, 4)\n",
"[Point(1, 2), Point(3, 4)]\n"
]
}
],
"prompt_number": 187
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Adding support for +** "
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x = 1\n",
"y = 2\n",
"print x+y"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"3\n"
]
}
],
"prompt_number": 189
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x.__add__(y)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 190,
"text": [
"3"
]
}
],
"prompt_number": 190
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"class Point3:\n",
" def __init__(self, x, y):\n",
" self.x = x\n",
" self.y = y\n",
" \n",
" def __add__(self, p):\n",
" return Point3(self.x+p.x, self.y+p.y)\n",
" \n",
" def __str__(self):\n",
" return \"(%s, %s)\" % (self.x, self.y)\n",
" \n",
" def __repr__(self):\n",
" return \"Point(%s, %s)\" % (self.x, self.y)\n",
" \n",
"p1 = Point3(1, 2)\n",
"p2 = Point3(3, 4)\n",
"print p1, p2\n",
"print [p1, p2]\n",
"print p1+p2"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(1, 2) (3, 4)\n",
"[Point(1, 2), Point(3, 4)]\n",
"(4, 6)\n"
]
}
],
"prompt_number": 192
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"What happens when we call a function?\n",
"\n",
" square(5)"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"square.__call__(5)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 193,
"text": [
"25"
]
}
],
"prompt_number": 193
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x = [1, 2, 3, 4]\n",
"x[3]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 194,
"text": [
"4"
]
}
],
"prompt_number": 194
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x.__getitem__(3)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 195,
"text": [
"4"
]
}
],
"prompt_number": 195
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"class Adder:\n",
" def __init__(self, x):\n",
" self.x = x\n",
" \n",
" def __call__(self, y):\n",
" return self.x + y\n",
"\n",
"add5 = Adder(5)\n",
"print add5(4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"9\n"
]
}
],
"prompt_number": 196
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Implement `logtime` decorator as a class with `__call__` method."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Remember that, the following:\n",
"\n",
" @logtime\n",
" def timepass():\n",
" ...\n",
" \n",
" print timepass()\n",
"\n",
"is equivalant to:\n",
"\n",
" def timepass():\n",
" ...\n",
" \n",
" timepass = logtime(timepass)\n",
" \n",
" print timepass()\n",
" \n",
"So, the constructor of logtime class get the function as argument."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [],
"language": "python",
"metadata": {},
"outputs": []
}
],
"metadata": {}
}
]
}
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