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#+LaTeX_HEADER: \usepackage{listings}

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

#+LaTeX_HEADER:  commentstyle=\color{red}\itshape, stringstyle=\color{darkgreen},

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#+TITLE:  Getting started with functions

#+AUTHOR:  FOSSEE

#+EMAIL:   info@fossee.in

#+DATE:    

#+DESCRIPTION: 

#+KEYWORDS: 

#+LANGUAGE:  en

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

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

# * Outline

#   - Manipulating one and multi dimensional arrays

#   - Access and change individual elements 

#   - Access and change rows and columns 

#   - Slicing and striding on arrays to access chunks 

#   - Read images into arrays and manipulations

# * Sample Arrays

#   #+begin_src python

#     In []: A = array([12, 23, 34, 45, 56])

#     In []: C = array([[11, 12, 13, 14, 15],

#                       [21, 22, 23, 24, 25],

#                       [31, 32, 33, 34, 35],

#                       [41, 42, 43, 44, 45],

#                       [51, 52, 53, 54, 55]])

#   #+end_src

# * Question 1

#   Change the last column of ~C~ to zeroes. 

# * Solution 1

#   #+begin_src python

#     In []:  C[:, -1] = 0

#   #+end_src

# * Question 2

#   Change ~A~ to ~[11, 12, 13, 14, 15]~. 

# * Solution 2

#   #+begin_src python

#     In []:  A[:] = [11, 12, 13, 14, 15]

#   #+end_src

# * squares.png

#   #+begin_latex

#     \begin{center}

#       \includegraphics[scale=0.6]{squares}    

#     \end{center}

#   #+end_latex

# * Question 3

#   - obtain ~[22, 23]~ from ~C~. 

#   - obtain ~[11, 21, 31, 41]~ from ~C~. 

#   - obtain ~[21, 31, 41, 0]~.   

# * Solution 3

#   #+begin_src python

#     In []:  C[1, 1:3]

#     In []:  C[0:4, 0]

#     In []:  C[1:5, 0]

#   #+end_src

# * Question 4

#   Obtain ~[[23, 24], [33, -34]]~ from ~C~

# * Solution 4

#   #+begin_src python

#     In []:  C[1:3, 2:4]

#   #+end_src

# * Question 5

#   Obtain the square in the center of the image

# * Solution 5

#   #+begin_src python

#     In []: imshow(I[75:225, 75:225])

#   #+end_src

# * Question 6

#   Obtain the following

#   #+begin_src python

#     [[12, 0], [42, 0]]

#     [[12, 13, 14], [0, 0, 0]]

#   #+end_src

# * Solution 6

#   #+begin_src python

#     In []: C[::3, 1::3]

#     In []: C[::4, 1:4]

#   #+end_src

# * Summary

#   You should now be able to --

#   - Manipulate 1D \& Multi dimensional arrays

#       - Access and change individual elements 

#       - Access and change rows and columns 

#       - Slice and stride on arrays

#   - Read images into arrays and manipulate them.

* Outline

  - Define functions

  - Pass arguments to functions

  - Learn about docstrings

  - Return values from functions

* Function

  - Eliminate code redundancy

  - Help in code reuse

  - Subroutine

    - relatively independent of remaining code

* ~f(x)~ a mathematical function

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

  : f(1) -> 1

  : f(2) -> 4

* Define ~f(x)~ in Python

  #+begin_src python

    def f(x):

        return x*x

  #+end_src

  - ~def~ - keyword

  - ~f~ - function name

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

* Exercise 1

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

  number ~n~.

  - Pause here and try to solve the problem yourself.

* Solution

  #+begin_src python

    def cube(n):

    	return n**3

  #+end_src

* ~greet~ function

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

 #+begin_src python

    def greet():

    	print "Hello World!"

 #+end_src

  - Call the function ~greet~

    : In []: greet()

    : Hello World!

* Exercise 2

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

  ~a~ and ~b~.

  - Pause here and try to solve the problem yourself.

* Solution 2

 #+begin_src python

    def avg(a,b):

    	return (a + b)/2

 #+end_src

 - ~a~ and ~b~ are parameters

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

* Docstring

  - Documenting/commenting code is a good practice

   #+begin_src python

     def avg(a,b):

         """ avg takes two numbers as input 

	 (a & b), and returns the average 

	 of a and b"""

	 return (a+b)/2

   #+end_src

  - Docstring

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

    - Inside triple quote.

  - Documentation

    : avg?

* Exercise 3

  Add docstring to the function f.

* Solution 3

#+begin_src python

  def f(x):

      """Accepts a number x as argument and,

      returns the square of the number x."""

      return x*x

#+end_src

* Exercise 4

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

  perimeter of a circle given radius ~r~.

* Solution 4

#+begin_src python

  def circle(r):

      """returns area and perimeter of a circle given 

      radius r"""

      pi = 3.14

      area = pi * r * r

      perimeter = 2 * pi * r

      return area, perimeter

#+end_src

* ~what~

#+begin_src python

 def what( n ):

     if n < 0: n = -n

     while n > 0:

         if n % 2 == 1:

             return False

         n /= 10

     return True

#+end_src

* ~even_digits~

#+begin_src python

 def even_digits( n ):

    """returns True if all the digits of number 

    n is even returns False if all the digits 

    of number n is not even"""

     if n < 0: n = -n

     while n > 0:

         if n % 2 == 1:

             return False

         n /= 10

     return True

#+end_src

* ~what~

#+begin_src python

 def what( n ):

     i = 1

     while i * i < n:

         i += 1

     return i * i == n, i

#+end_src

* ~is_perfect_square~

#+begin_src python

 def is_perfect_square( n ):

     """returns True and square root of n, 

     if n is a perfect square, otherwise 

     returns False and the square root 

     of the next perfect square"""

     i = 1

     while i * i < n:

         i += 1

     return i * i == n, i

#+end_src

* Summary

 - Functions in Python

 - Passing parameters to a function

 - Returning values from a function

 - We also did few code reading exercises.

* Thank you!

#+begin_latex

  \begin{block}{}

  \begin{center}

  This spoken tutorial has been produced by the

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

  \end{center}

  \begin{center}

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

      Information \& Communication Technology \\ 

      MHRD, Govt. of India}.

  \end{center}  

  \end{block}

#+end_latex