diff -r 88a01948450d -r d33698326409 getting_started_with_functions/script.rst
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/getting_started_with_functions/script.rst	Wed Dec 01 16:51:35 2010 +0530
@@ -0,0 +1,293 @@
+.. Objectives
+.. ----------
+
+.. 8.1 LO: getting started with functions (3)
+
+.. At the end of this tutorial, you will be able to 
+
+.. 1. define function
+.. #. define functions with arguments
+.. #. learn about docstrings
+.. #. learn about return values
+..     can return multiple values
+.. #. read code
+
+
+.. Prerequisites
+.. -------------
+
+..   1. should have ``ipython`` installed. 
+..   #. getting started with ``ipython``.
+
+     
+.. Author              : Anoop Jacob Thomas <anoop@fossee.in>
+   Internal Reviewer   : 
+   External Reviewer   :
+   Language Reviewer   : Bhanukiran
+   Checklist OK?       : <put date stamp here, not OK> [2010-10-05]
+
+
+==============================
+Getting started with functions
+==============================
+
+{{{ show welcome slide }}}
+
+Hello and welcome to the tutorial getting started with functions.
+
+{{{ switch to next slide, outline slide }}}
+
+In this tutorial we will learn about functions in python, how to
+define functions, arguments to functions, docstrings, and function
+return value.
+
+{{{ switch to next slide, Function }}}
+
+While writing code, we always want to reduce the number of lines of
+code and functions is a way of reusing the code. Thus the same lines
+of code can be used as many times as needed. A function is a portion of code
+within a larger program that performs a specific task and is
+relatively independent of the remaining code. Now let us get more
+familiar with functions,
+
+{{{ switch to next slide, f(x) a mathematical function }}}
+
+Consider a mathematical function f(x) = x square. Here x is a variable
+and with different values of x the value of function will change. When
+x is one f(1) will return the value 1 and f(2) will return us the
+value 4. Let us now see how to define the function f(x) in python.
+
+{{{ switch to next slide, define f(x) in Python }}}
+
+In your Ipython interpreter type the following,
+::
+
+    def f(x):
+    	return x*x
+
+Well that defined the function, so before learning what we did let us
+see if it returns the expected values, try,
+::
+
+    f(1)
+    f(2)
+
+Yes, it returned 1 and 4 respectively. And now let us see what we did.
+We wrote two lines: The first line ``def f(x)`` is used to define the
+name and the parameters to the function and the second line is used to
+fix what the function is supposed to return. ``def`` is a keyword and
+``f`` is the name of the function and ``x`` the parameter of the
+function.
+
+{{{ switch to next slide, problem statement 1 }}}
+
+%% 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.
+
+{{{ switch to next slide, solution }}}
+
+The problem can be solved as,
+::
+
+    def cube(n):
+    	return n**3
+
+And now let us see how to write functions without arguments.
+
+{{{ switch to next slide, greet function }}}
+
+let us define a new function called ``greet`` which will print ``Hello
+World``.
+::
+
+    def greet():
+    	print "Hello World!"
+
+now try calling the function,
+::
+
+    greet()
+
+Well that is a function which takes no arguments. Also note that it is
+not mandatory for a function to return values. The function ``greet``
+neither takes any argument nor returns any value.
+
+Now let us see how to write functions with more than one argument.
+
+{{{ switch to next slide, exercise 2 }}}
+
+%% 2 %% Write a python function named ``avg`` which computes the
+   average of ``a`` and ``b``.
+
+Pause here and try to solve the problem yourself.
+
+{{{ switch to next slide, solution 2 }}}
+
+The problem can be solved as,
+::
+
+    def avg(a,b):
+    	return (a + b)/2
+
+Thus if we want a function to accept more arguments, we just list them
+separated with a comma between the parenthesis after the function's name
+in the ``def`` line.
+
+{{{ switch to next slide, docstring }}}
+
+It is always a good practice to document the code that we write, and
+for a function we define we should write an abstract of what the
+function does, and that is called a docstring. Let us modify the
+function ``avg`` and add docstring to it. Do the following,
+::
+
+    def avg(a,b):
+        """ avg takes two numbers as input (a & b), and
+	returns the average of a and b"""
+	return (a+b)/2
+
+Note that docstrings are entered in the immediate line after the
+function definition and put as a triple quoted string. And here as far
+as the code functionality is concerned, we didn't do anything. We just
+added an abstract of what the function does.
+
+Now try this in the ipython interpreter.
+::
+
+    avg?
+
+It displays the docstring as we gave it. Thus docstring is a good way
+of documenting the function we write.
+
+Try to do this,
+::
+
+    f?
+
+It doesn't have a docstring associated with it. Also we cannot infer
+anything from the function name, and thus we are forced to read the
+code to understand about the function.
+
+{{{ switch to next slide, exercise 3 }}}
+
+%% 3 %% Add docstring to the function f.
+
+Pause here and try to do it yourself.
+
+{{{ switch to next slide, solution }}}
+
+We need to define the function again to add docstring to the function
+``f`` and we do it as,
+::
+
+    def f(x):
+    	"""Accepts a number x as argument and,
+	returns the square of the number x."""
+	return x*x
+
+{{{ switch to next slide, exercise 4 }}}
+
+%% 4 %% Write a python function named ``circle`` which returns the
+   area and perimeter of a circle given radius ``r``.
+
+Pause here and try to solve the problem yourself.
+
+{{{ switch to next slide, solution 4 }}}
+
+The problem requires us to return two values instead of one which we
+were doing till now. We can solve the problem as,
+::
+
+    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
+
+A python function can return any number of values. There is no
+restriction for it.
+
+Let us call the function ``circle`` as,
+::
+
+    a, p = circle(6)
+    print a
+    print p
+
+Now we have done enough coding, let us do some code reading exercise,
+
+{{{ switch to next slide, what }}}
+
+What does the function ``what`` do?
+
+.. def what( n ):
+..     if n < 0: n = -n
+..     while n > 0:
+..         if n % 2 == 1:
+..             return False
+..         n /= 10
+..     return True
+
+Pause here and try to figure out what the function ``what`` does.
+
+{{{ switch to next slide, even_digits }}}
+
+.. def even_digits( n ):
+..    """returns True if all the digits in the number n are even,
+..    returns False if all the digits in the number n are not even"""
+..     if n < 0: n = -n
+..     while n > 0:
+..         if n % 2 == 1:
+..             return False
+..         n /= 10
+..     return True
+
+The function returns ``True`` if all the digits of the number ``n``
+are even, otherwise it returns ``False``.
+
+Now one more code reading exercise,
+
+{{{ switch to next slide, what }}}
+
+What does the function ``what`` do?
+
+.. def what( n ):
+..     i = 1
+..     while i * i < n:
+..         i += 1
+..     return i * i == n, i
+
+Pause here and try to figure out what the function ``what`` does.
+
+{{{ switch to next slide, is_perfect_square }}}
+
+.. 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
+
+
+The function returns ``True`` and the square root of ``n`` if n is a
+perfect square, otherwise it returns ``False`` and the square root of
+the next perfect square.
+
+This brings us to the end of this tutorial, in this tutorial we covered
+
+{{{ switch to next slide, summary }}}
+
+- Functions in Python
+- Passing parameters to a function
+- Returning values from a function
+
+We also did few code reading exercises.
+
+{{{ switch to next slide, Thank you }}}
+
+Thank you!