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    14 

    15 #+LaTeX_HEADER: \usepackage{listings}

    16 

    17 #+LaTeX_HEADER:\lstset{language=Python, basicstyle=\ttfamily\bfseries,

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    19 #+LaTeX_HEADER:  showstringspaces=false, keywordstyle=\color{blue}\bfseries}

    20 

    21 #+TITLE:  Getting started with functions

    22 #+AUTHOR:  FOSSEE

    23 #+EMAIL:   info@fossee.in

    24 #+DATE:    

    25 

    26 #+DESCRIPTION: 

    27 #+KEYWORDS: 

    28 #+LANGUAGE:  en

    29 #+OPTIONS:   H:3 num:nil toc:nil \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t

    30 #+OPTIONS:   TeX:t LaTeX:nil skip:nil d:nil todo:nil pri:nil tags:not-in-toc

    31 

    32 * Outline

    33   - Define functions

    34   - Pass arguments to functions

    35   - Learn about docstrings

    36   - Return values from functions

    37 

    38 * Function

    39   - Eliminate code redundancy

    40   - Help in code reuse

    41   - Subroutine

    42     - relatively independent of remaining code

    43 

    44 * ~f(x)~ a mathematical function

    45 

    46   $f(x) = x^{2}$

    47 

    48   : f(1) -> 1

    49   : f(2) -> 4

    50 

    51 * Define ~f(x)~ in Python

    52   #+begin_src python

    53     def f(x):

    54         return x*x

    55   #+end_src

    56 

    57   - ~def~ - keyword

    58   - ~f~ - function name

    59   - ~x~ - parameter / argument to function ~f~

    60 

    61 * Exercise 1

    62 

    63   Write a python function named ~cube~ which computes the cube of a given

    64   number ~n~.

    65   

    66   - Pause here and try to solve the problem yourself.

    67 

    68 * Solution

    69   #+begin_src python

    70     def cube(n):

    71     	return n**3

    72   #+end_src

    73 

    74 * ~greet~ function

    75 

    76  Function ~greet~ which will print ~Hello World!~.

    77  #+begin_src python

    78     def greet():

    79     	print "Hello World!"

    80  #+end_src

    81   - Call the function ~greet~

    82     : In []: greet()

    83     : Hello World!

    84 

    85 * Exercise 2

    86 

    87   Write a python function named ~avg~ which computes the average of

    88   ~a~ and ~b~.

    89 

    90   - Pause here and try to solve the problem yourself.

    91 

    92 * Solution 2

    93  #+begin_src python

    94     def avg(a,b):

    95     	return (a + b)/2

    96  #+end_src

    97 

    98  - ~a~ and ~b~ are parameters

    99  - ~def f(p1, p2, p3, ... , pn)~

   100 

   101 * Docstring

   102 

   103   - Documenting/commenting code is a good practice

   104    #+begin_src python

   105      def avg(a,b):

   106          """ avg takes two numbers as input 

   107 	 (a & b), and returns the average 

   108 	 of a and b"""

   109 	 return (a+b)/2

   110    #+end_src

   111   - Docstring

   112     - written in the line after the ~def~ line.

   113     - Inside triple quote.

   114   - Documentation

   115     : avg?

   116 * Exercise 3

   117   Add docstring to the function f.

   118 

   119 * Solution 3

   120 

   121 #+begin_src python

   122   def f(x):

   123       """Accepts a number x as argument and,

   124       returns the square of the number x."""

   125       return x*x

   126 #+end_src

   127 

   128 * Exercise 4

   129   Write a python function named ~circle~ which returns the area and

   130   perimeter of a circle given radius ~r~.

   131 

   132 * Solution 4

   133 #+begin_src python

   134   def circle(r):

   135       """returns area and perimeter of a circle given 

   136       radius r"""

   137       pi = 3.14

   138       area = pi * r * r

   139       perimeter = 2 * pi * r

   140       return area, perimeter

   141 #+end_src

   142 

   143 * ~what~

   144 #+begin_src python

   145 

   146  def what( n ):

   147      if n < 0: n = -n

   148      while n > 0:

   149          if n % 2 == 1:

   150              return False

   151          n /= 10

   152      return True

   153 #+end_src

   154 

   155 * ~even_digits~

   156 #+begin_src python

   157  def even_digits( n ):

   158     """returns True if all the digits of number 

   159     n is even returns False if all the digits 

   160     of number n is not even"""

   161      if n < 0: n = -n

   162      while n > 0:

   163          if n % 2 == 1:

   164              return False

   165          n /= 10

   166      return True

   167 #+end_src

   168 

   169 * ~what~

   170 #+begin_src python

   171  def what( n ):

   172      i = 1

   173      while i * i < n:

   174          i += 1

   175      return i * i == n, i

   176 #+end_src

   177 

   178 * ~is_perfect_square~

   179 #+begin_src python

   180  def is_perfect_square( n ):

   181      """returns True and square root of n, 

   182      if n is a perfect square, otherwise 

   183      returns False and the square root 

   184      of the next perfect square"""

   185      i = 1

   186      while i * i < n:

   187          i += 1

   188      return i * i == n, i

   189 #+end_src

   190 

   191 * Summary

   192  - Functions in Python

   193  - Passing parameters to a function

   194  - Returning values from a function

   195 

   196  - We also did few code reading exercises.

   197 

   198 * Thank you!

   199 #+begin_latex

   200   \begin{block}{}

   201   \begin{center}

   202   This spoken tutorial has been produced by the

   203   \textcolor{blue}{FOSSEE} team, which is funded by the 

   204   \end{center}

   205   \begin{center}

   206     \textcolor{blue}{National Mission on Education through \\

   207       Information \& Communication Technology \\ 

   208       MHRD, Govt. of India}.

   209   \end{center}  

   210   \end{block}

   211 #+end_latex