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Python Training - September 26-28, 2013
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day1.ipynb
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day2.ipynb
{
"metadata": {
"name": ""
},
"nbformat": 3,
"nbformat_minor": 0,
"worksheets": [
{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Python Training - Day 2"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Functions in more detail**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# Passing arguments by name\n",
"def difference(x, y):\n",
" return x-y\n",
"\n",
"print difference(5, 3)\n",
"print difference(x=5, y=3)\n",
"print difference(y=3, x=5)\n",
"print difference(5, y=3)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2\n",
"2\n",
"2\n",
"2\n"
]
}
],
"prompt_number": 5
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# default arguments\n",
"def incr(x, amount=1):\n",
" return x + amount\n",
"\n",
"print incr(5)\n",
"print incr(5, 3)\n",
"print incr(5, amount=3)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"6\n",
"8\n",
"8\n"
]
}
],
"prompt_number": 9
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def find_person(name=None, email=None, company=None, year=None):\n",
" pass\n",
"\n",
"find_person(\"joe\", None, \"Foo\", None)\n",
"find_person(name=\"joe\", company=\"Foo\")"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 12
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file circle.py\n",
"\n",
"pi = 3.14\n",
"\n",
"def area(r):\n",
" return pi * square(r)\n",
"\n",
"def square(x):\n",
" return x * x \n",
"\n",
"print area(10)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing circle.py\n"
]
}
],
"prompt_number": 15
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python circle.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"314.0\r\n"
]
}
],
"prompt_number": 16
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file square2.py\n",
"\n",
"\n",
"def square(x):\n",
" y = x * x\n",
" return y\n",
"\n",
"y = 4\n",
"y2 = square(y)\n",
"print y, y2\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting square2.py\n"
]
}
],
"prompt_number": 25
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python square2.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"4 16\r\n"
]
}
],
"prompt_number": 26
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Tuples**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"(1, 2)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 27,
"text": [
"(1, 2)"
]
}
],
"prompt_number": 27
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x = (1, 2, 3, 4, 5)"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 28
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"len(x)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 29,
"text": [
"5"
]
}
],
"prompt_number": 29
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x[1]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 30,
"text": [
"2"
]
}
],
"prompt_number": 30
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x[1:4]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 31,
"text": [
"(2, 3, 4)"
]
}
],
"prompt_number": 31
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x[0] = 3"
],
"language": "python",
"metadata": {},
"outputs": [
{
"ename": "TypeError",
"evalue": "'tuple' object does not support item assignment",
"output_type": "pyerr",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mTypeError\u001b[0m Traceback (most recent call last)",
"\u001b[0;32m<ipython-input-32-4e9f9c7cce1d>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mx\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m0\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;36m3\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[0;31mTypeError\u001b[0m: 'tuple' object does not support item assignment"
]
}
],
"prompt_number": 32
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"tuple(range(10))"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 33,
"text": [
"(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)"
]
}
],
"prompt_number": 33
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"a, b = 1, 2"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 34
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"1, 2"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 35,
"text": [
"(1, 2)"
]
}
],
"prompt_number": 35
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x = 1, 2, 3"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 36
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 37,
"text": [
"(1, 2, 3)"
]
}
],
"prompt_number": 37
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"a, b, c = x"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 38
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print a, b, c"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1 2 3\n"
]
}
],
"prompt_number": 39
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"a, b = b, a"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 40
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print a, b"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"2 1\n"
]
}
],
"prompt_number": 41
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x[1:]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 42,
"text": [
"(2, 3)"
]
}
],
"prompt_number": 42
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# list of tuples\n",
"\n",
"x = [(1, 1), (2, 4), (3, 9)]"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 43
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"for a in x:\n",
" print a, a[0], a[1]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(1, 1) 1 1\n",
"(2, 4) 2 4\n",
"(3, 9) 3 9\n"
]
}
],
"prompt_number": 47
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"for a, b in x:\n",
" print a, b"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1 1\n",
"2 4\n",
"3 9\n"
]
}
],
"prompt_number": 45
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"a, b = x[0]\n",
"print a, b"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1 1\n"
]
}
],
"prompt_number": 46
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Sorting Lists"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"x = [2, 10, 8, 4, 98]\n",
"x.sort() # modifies list in-place\n",
"print x"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[2, 4, 8, 10, 98]\n"
]
}
],
"prompt_number": 51
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"y = [2, 10, 8, 4, 98]\n",
"print sorted(y) # returns a new list in sorted order\n",
"print y"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[2, 4, 8, 10, 98]\n",
"[2, 10, 8, 4, 98]\n"
]
}
],
"prompt_number": 53
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Lets try to find if python sort is fast enough to sort a million values.\n"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"import random\n",
"import string\n",
"import time\n",
"def random_string(n):\n",
" return \"\".join([random.choice(string.letters) for i in range(n)])\n",
"\n",
"print \"generating strings\"\n",
"names = [random_string(100) for i in range(10000)] * 100\n",
"\n",
"print \"sorting...\"\n",
"t0 = time.time()\n",
"names.sort()\n",
"t1 = time.time()\n",
"print \"took\", t1-t0, \"seconds\""
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"generating strings\n",
"sorting..."
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
"\n",
"took"
]
},
{
"output_type": "stream",
"stream": "stdout",
"text": [
" 0.669486045837 seconds\n"
]
}
],
"prompt_number": 63
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"names = ['c', 'Java', 'Python', 'haskell', \n",
" 'perl', 'go']\n",
"print sorted(names)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"['Java', 'Python', 'c', 'go', 'haskell', 'perl']\n"
]
}
],
"prompt_number": 70
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# How to sort these names by length?\n",
"# How to sort these ignorng the case?"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 68
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print sorted(names, key=len)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"['c', 'go', 'Java', 'perl', 'Python', 'haskell']\n"
]
}
],
"prompt_number": 71
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def lower(s): return s.lower()\n",
"\n",
"print sorted(names, key=lower)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"['c', 'go', 'haskell', 'Java', 'perl', 'Python']\n"
]
}
],
"prompt_number": 73
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"scores = [(\"A\", 20), \n",
" (\"C\", 43),\n",
" (\"B\", 53), \n",
" (\"D\", 12)]\n",
"\n",
"def f(x):\n",
" # fix this\n",
" return x[1]\n",
"\n",
"# print them in the order of scores\n",
"for name, score in sorted(scores, key=f):\n",
" print score, name"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"12 D\n",
"20 A\n",
"43 C\n",
"53 B\n"
]
}
],
"prompt_number": 79
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# lambda functions\n",
"\n",
"print sorted(scores, key=lambda x: x[1])"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[('D', 12), ('A', 20), ('C', 43), ('B', 53)]\n"
]
}
],
"prompt_number": 81
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"square = lambda x:x*x\n",
"print square(4)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"16\n"
]
}
],
"prompt_number": 82
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"g = lambda x: x[1]\n",
"print g((\"a\", 3, 5))"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"3\n"
]
}
],
"prompt_number": 84
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Working with Files"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file a.txt\n",
"first line \n",
"second line\n",
"third line\n",
"fourth line\n",
"fifth line"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing a.txt\n"
]
}
],
"prompt_number": 86
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print open(\"a.txt\").read()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"first line \n",
"second line\n",
"third line\n",
"fourth line\n",
"fifth line\n"
]
}
],
"prompt_number": 87
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"open(\"a.txt\").read()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 88,
"text": [
"'first line \\nsecond line\\nthird line\\nfourth line\\nfifth line'"
]
}
],
"prompt_number": 88
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"open(\"a.txt\").readlines()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 89,
"text": [
"['first line \\n',\n",
" 'second line\\n',\n",
" 'third line\\n',\n",
" 'fourth line\\n',\n",
" 'fifth line']"
]
}
],
"prompt_number": 89
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# creating a file with 100 numbers\n",
"!seq 100 > numbers.txt"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 90
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file head.py\n",
"# Program to print first 10 lines of a file.\n",
"# The filename will be passed as command line \n",
"# argument.\n",
"import sys\n",
"filename = sys.argv[1]\n",
"for line in open(filename).readlines()[:10]:\n",
" print line.strip(\"\\n\")\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting head.py\n"
]
}
],
"prompt_number": 97
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python head.py numbers.txt"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1\r\n",
"2\r\n",
"3\r\n",
"4\r\n",
"5\r\n",
"6\r\n",
"7\r\n",
"8\r\n",
"9\r\n",
"10\r\n"
]
}
],
"prompt_number": 98
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a program `tail.py` to print the last 10 lines of a file. The program should take the filename as command line argument.\n",
"\n",
" $ python tail.py numbers.txt"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a program `grep.py` to print all the lines containing given pattern. The program should take the pattern and filename as arguments.\n",
"\n",
" $ python grep.py 0 numbers.txt\n",
" 10\n",
" 20\n",
" ...\n",
" \n",
" $ python grep.py def square.py\n",
" def square(x):"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Writing files**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# open file in write mode\n",
"f = open(\"b.txt\", \"w\")\n",
"f.write(\"hello world\\n\")\n",
"f.close()"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 99
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# reading the file that we just wrote\n",
"open(\"b.txt\").read()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 101,
"text": [
"'hello world\\n'"
]
}
],
"prompt_number": 101
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Wrire a program `copyfile.py` that takes 2 filenames as arguments and copies the first file into the second.\n",
"\n",
" $ python copyfile.py b.txt b2.txt"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file copyfile.py\n",
"\n",
"import sys\n",
"\n",
"filename1 = sys.argv[1]\n",
"filename2 = sys.argv[2]\n",
"\n",
"# reading the contents of the first file\n",
"contents = open(filename1).read()\n",
"\n",
"# writing the contents to the second file\n",
"f = open(filename2, \"w\")\n",
"f.write(contents)\n",
"f.close()\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing copyfile.py\n"
]
}
],
"prompt_number": 102
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## List Comprehensions"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"[x*x for x in range(10)]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 103,
"text": [
"[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]"
]
}
],
"prompt_number": 103
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def squares(numbers):\n",
" return [x*x for x in numbers]\n",
" \n",
"print squares(range(10))\n",
"print sum(squares(range(100)))"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]\n",
"328350\n"
]
}
],
"prompt_number": 107
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"numbers = range(10)\n",
"[x*x for x in numbers]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 108,
"text": [
"[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]"
]
}
],
"prompt_number": 108
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# Compute squares of all even numbes below 10\n",
"[x*x for x in numbers if x % 2 == 0]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 109,
"text": [
"[0, 4, 16, 36, 64]"
]
}
],
"prompt_number": 109
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# sum of squares of all even numbers below 100\n",
"print sum([x*x for x in range(100) if x % 2 == 0])"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"161700\n"
]
}
],
"prompt_number": 110
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** How do you find the length of longest string in a given list?\n",
"\n",
" names = ['c', 'Java', 'Python', 'haskell', \n",
" 'perl', 'go']\n",
" # ??"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Example: Parsing CSV file"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file a.csv\n",
"1,2,3\n",
"1,4,9\n",
"1,8,27"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing a.csv\n"
]
}
],
"prompt_number": 111
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"rows = [line.strip().split(\",\") \n",
" for line in open(\"a.csv\").readlines()]"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 119
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"rows"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 120,
"text": [
"[['1', '2', '3'], ['1', '4', '9'], ['1', '8', '27']]"
]
}
],
"prompt_number": 120
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print rows[0]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"['1', '2', '3']\n"
]
}
],
"prompt_number": 121
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print rows[0][2]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"3\n"
]
}
],
"prompt_number": 123
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file b.csv\n",
"# this is csv file with comments\n",
"# every line starting with # is a comment\n",
"1,2,3\n",
"1,4,9\n",
"1,8,27\n",
"# end of file"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing b.csv\n"
]
}
],
"prompt_number": 124
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Can you improve the previously written CSV parser to ignore comments?"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"rows = [line.strip().split(\",\") \n",
" for line in open(\"b.csv\").readlines()\n",
" if not line.startswith(\"#\")]\n",
"print rows"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"[['1', '2', '3'], ['1', '4', '9'], ['1', '8', '27']]\n"
]
}
],
"prompt_number": 126
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"How do you find sum of the last column?"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# first row\n",
"rows[0]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 128,
"text": [
"['1', '2', '3']"
]
}
],
"prompt_number": 128
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# last element of first row\n",
"rows[0][-1]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 129,
"text": [
"'3'"
]
}
],
"prompt_number": 129
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# last element of all rows (or the last column)\n",
"[row[-1] for row in rows]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 130,
"text": [
"['3', '9', '27']"
]
}
],
"prompt_number": 130
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# last column as ints\n",
"[int(row[-1]) for row in rows]"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 132,
"text": [
"[3, 9, 27]"
]
}
],
"prompt_number": 132
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# sum of last column\n",
"sum([int(row[-1]) for row in rows])"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 133,
"text": [
"39"
]
}
],
"prompt_number": 133
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Example: wordcount**"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Write a program `wc.py` to compute number of lines, number of words and number of characters in a file. "
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# It should work like unix command wc\n",
"!wc square.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
" 8 18 126 square.py\r\n"
]
}
],
"prompt_number": 142
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file wc.py\n",
"import sys\n",
"\n",
"def linecount(filename):\n",
" return len(open(filename).readlines())\n",
"\n",
"def wordcount(filename):\n",
" return len(open(filename).read().split())\n",
"\n",
"def charcount(filename):\n",
" return len(open(filename).read())\n",
"\n",
"f = sys.argv[1]\n",
"print linecount(f), wordcount(f), charcount(f), f\n",
" \n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting wc.py\n"
]
}
],
"prompt_number": 147
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python wc.py square.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"8 18 126 square.py\r\n"
]
}
],
"prompt_number": 148
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**The `os` module**"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"import os"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 149
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# get the current working directory\n",
"os.getcwd()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 150,
"text": [
"'/Users/anand/Dropbox/Trainings/2013/python-sept2013/notebook'"
]
}
],
"prompt_number": 150
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# list all files in testdir/\n",
"os.listdir(\"testdir\")"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 152,
"text": [
"['a.csv', 'b.csv', 'numbers.txt']"
]
}
],
"prompt_number": 152
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Write a program `listdir.py`, that takes name of a directory as command line argument and prints names of all the files in that directory.\n",
"\n",
"<pre>\n",
" $ python listdir.py /tmp\n",
" ...\n",
" $ python listdir.py c:\\Python27\n",
" ... \n",
"</pre>"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file listdir.py\n",
"import sys\n",
"import os\n",
"\n",
"dirname = sys.argv[1]\n",
"files = os.listdir(dirname)\n",
"for f in files:\n",
" print f"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Writing listdir.py\n"
]
}
],
"prompt_number": 153
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python listdir.py testdir"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"a.csv\r\n",
"b.csv\r\n",
"numbers.txt\r\n"
]
}
],
"prompt_number": 154
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Find the total number of lines in all the python files in the current directory."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file countcode.py\n",
"import os\n",
"\n",
"def linecount(filename):\n",
" return len(open(filename).readlines())\n",
"\n",
"# find files in the current dir\n",
"files = os.listdir(\".\") \n",
"\n",
"# find python files from files\n",
"pyfiles = [f for f in files if f.endswith(\".py\")]\n",
"\n",
"# find number of lines in each file\n",
"counts = [linecount(f) for f in pyfiles]\n",
"\n",
"# and fine the total\n",
"print sum(counts)\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting countcode.py\n"
]
}
],
"prompt_number": 159
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python countcode.py"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"93\r\n"
]
}
],
"prompt_number": 160
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"def linecount(filename):\n",
" return len(open(filename).readlines())\n",
"\n",
"print sum([linecount(f) for f in os.listdir(\".\") \n",
" if f.endswith(\".py\")])"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"93\n"
]
}
],
"prompt_number": 162
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Dictionaries"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d = {\"x\": 1, \"y\": 20}"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 163
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print d['x']"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"1\n"
]
}
],
"prompt_number": 164
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"person = {\n",
" \"name\": \"Anand\", \n",
" \"email\": \"[email protected]\",\n",
" \"phone\": \"00000000\"\n",
"}"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 172
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"person['name']"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 167,
"text": [
"'Anand'"
]
}
],
"prompt_number": 167
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 168,
"text": [
"{'x': 1, 'y': 20}"
]
}
],
"prompt_number": 168
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d.keys()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 169,
"text": [
"['y', 'x']"
]
}
],
"prompt_number": 169
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d.values()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 170,
"text": [
"[20, 1]"
]
}
],
"prompt_number": 170
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d.items()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 171,
"text": [
"[('y', 20), ('x', 1)]"
]
}
],
"prompt_number": 171
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print person"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"{'phone': '00000000', 'name': 'Anand', 'email': '[email protected]'}\n"
]
}
],
"prompt_number": 173
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"print 'phone' in person"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"True\n"
]
}
],
"prompt_number": 174
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 175,
"text": [
"{'x': 1, 'y': 20}"
]
}
],
"prompt_number": 175
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d['x'] = 5"
],
"language": "python",
"metadata": {},
"outputs": [],
"prompt_number": 176
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"d"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 177,
"text": [
"{'x': 5, 'y': 20}"
]
}
],
"prompt_number": 177
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"# since 'x' is there in d, it gives d['x']\n",
"print d.get('x', 0)\n",
"\n",
"# since z is not there in d, it gives the default\n",
"print d.get('z', 0)"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"5\n",
"0\n"
]
}
],
"prompt_number": 179
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### Example: Word Freqency"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file wf.py\n",
"import sys\n",
"\n",
"def read_words(filename):\n",
" return open(filename).read().split()\n",
"\n",
"def wordfreq(words):\n",
" counts = {}\n",
" print \"begin\", counts\n",
" for w in words:\n",
" counts[w] = counts.get(w, 0) + 1\n",
" print w, counts\n",
" return counts\n",
"\n",
"def print_freq(freq):\n",
" print freq\n",
"\n",
"def main():\n",
" filename = sys.argv[1]\n",
" words = read_words(filename)\n",
" freq = wordfreq(words)\n",
" print_freq(freq)\n",
"\n",
"main()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting wf.py\n"
]
}
],
"prompt_number": 192
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file words.txt\n",
"one\n",
"one two\n",
"one two three\n",
"one two three four\n",
"one two three four five"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting words.txt\n"
]
}
],
"prompt_number": 193
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python wf.py words.txt"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"begin {}\r\n",
"one {'one': 1}\r\n",
"one {'one': 2}\r\n",
"two {'two': 1, 'one': 2}\r\n",
"one {'two': 1, 'one': 3}\r\n",
"two {'two': 2, 'one': 3}\r\n",
"three {'three': 1, 'two': 2, 'one': 3}\r\n",
"one {'three': 1, 'two': 2, 'one': 4}\r\n",
"two {'three': 1, 'two': 3, 'one': 4}\r\n",
"three {'three': 2, 'two': 3, 'one': 4}\r\n",
"four {'four': 1, 'three': 2, 'two': 3, 'one': 4}\r\n",
"one {'four': 1, 'three': 2, 'two': 3, 'one': 5}\r\n",
"two {'four': 1, 'three': 2, 'two': 4, 'one': 5}\r\n",
"three {'four': 1, 'three': 3, 'two': 4, 'one': 5}\r\n",
"four {'four': 2, 'three': 3, 'two': 4, 'one': 5}\r\n",
"five {'four': 2, 'three': 3, 'five': 1, 'two': 4, 'one': 5}\r\n",
"{'four': 2, 'three': 3, 'five': 1, 'two': 4, 'one': 5}\r\n"
]
}
],
"prompt_number": 194
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### String Formatting"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\"Hello %s\" % \"Foo\""
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 195,
"text": [
"'Hello Foo'"
]
}
],
"prompt_number": 195
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"\"Chapter %d: %s\" % (1, \"Getting started\")"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 196,
"text": [
"'Chapter 1: Getting started'"
]
}
],
"prompt_number": 196
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"'<a href=\"%s\">%s</a>' % (\"http://google.com\", \"http://google.com/\")"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 197,
"text": [
"'<a href=\"http://google.com\">http://google.com/</a>'"
]
}
],
"prompt_number": 197
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"'<a href=\"%(url)s\">%(url)s</a>' % {\"url\": \"http://google.com\"}"
],
"language": "python",
"metadata": {},
"outputs": [
{
"metadata": {},
"output_type": "pyout",
"prompt_number": 198,
"text": [
"'<a href=\"http://google.com\">http://google.com</a>'"
]
}
],
"prompt_number": 198
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Problem** Given a set of photographs, generate one html file for each photo to navigate through those photos. Each html file should have next and prev links.\n",
"\n",
"Sample photos and sample html file are available at <http://anandology.com/tmp/album.zip>."
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"%%file album.py\n",
"import sys\n",
"import os\n",
"\n",
"html = \"\"\"\n",
"<a href=\"#\">Prev</a> | <a href=\"#\">Next</a>\n",
"<br/>\n",
"<img src=\"%s\"/>\n",
"\"\"\"\n",
"\n",
"def find_jpg_files(dirname):\n",
" # fix this\n",
" return os.listdir(dirname)\n",
"\n",
"def generate_html(dirname, filename):\n",
" htmlfile = filename.replace(\".jpg\", \".html\")\n",
" path = os.path.join(dirname, htmlfile)\n",
" print \"generating\", htmlfile, path\n",
"\n",
"def main():\n",
" dirname = sys.argv[1]\n",
" files = find_jpg_files(dirname)\n",
" for f in files:\n",
" generate_html(dirname, f)\n",
" \n",
"main()"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"Overwriting album.py\n"
]
}
],
"prompt_number": 211
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"!python album.py /tmp/album"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"generating photo1.html /tmp/album/photo1.html\r\n",
"generating photo2.html /tmp/album/photo2.html\r\n",
"generating photo3.html /tmp/album/photo3.html\r\n",
"generating photo4.html /tmp/album/photo4.html\r\n",
"generating sample-photo2.html /tmp/album/sample-photo2.html\r\n"
]
}
],
"prompt_number": 212
},
{
"cell_type": "code",
"collapsed": false,
"input": [],
"language": "python",
"metadata": {},
"outputs": []
}
],
"metadata": {}
}
]
}
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