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#+TITLE:  Getting started with functions
#+AUTHOR:  FOSSEE
#+EMAIL:   info@fossee.in
#+DATE:    

#+DESCRIPTION: 
#+KEYWORDS: 
#+LANGUAGE:  en
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* 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
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  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