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+++ b/advanced-features-functions/script.rst Wed Oct 06 15:16:09 2010 +0530
@@ -0,0 +1,203 @@
+========
+ Script
+========
+
+{{{ show the welcome slide }}}
+
+Welcome to the tutorial on advanced feature of functions.
+
+{{{ show the outline slide }}}
+
+In this tutorial we shall be looking at specifying default arguments
+to functions when defining them and calling functions using keyword
+arguments. We shall also, look at some of the built-in functions
+available in the standard library of Python.
+
+{{{ switch to terminal }}}
+
+We have an ``ipython`` terminal open, which we shall be using through
+out this session.
+
+Let's use the ``round`` function as an example to understand what a
+default value of an argument means. Let's type the following
+expressions in the terminal.
+
+::
+
+ round(2.484)
+
+ round(2.484, 2)
+
+Both the first expression and the second are calls to the ``round``
+function, but the first calls it with only one argument and the second
+calls it with two arguments. By observing the output, we can guess
+that the first one is equivalent to call with the second argument
+being 0. 0 is the default value of the argument.
+
+{{{ show a slide with examples of functions showing default values }}}
+::
+
+ s.strip() # strips on spaces.
+ s.strip('@') # strips the string of '@' symbols.
+
+ plot(x, y) # plots with x vs. y using default line style.
+ plot(x, y, 'o') # plots x vs. y with circle markers.
+
+ linspace(0, 2*pi, 100) # returns 100 points between 0 and 2pi
+ linspace(0, 2*pi) # returns 50 points between 0 and 2pi
+
+#[punch: all above content goes on to a slide]
+
+{{{ switch back to ipython }}}
+
+Let's now define a simple function that uses default arguments. We
+define a simple function that prints a welcome message to a person,
+given a greeting and his/her name.
+
+::
+
+ def welcome(greet, name="World"):
+ print greet, name
+
+Let us first call the function with two arguments, one for ``greet``
+and other for ``name``.
+
+::
+
+ welcome("Hi", "Guido")
+
+We get the expected welcome message, "Hi Guido".
+
+Now let us call the function with just one argument "Hello".
+::
+
+ welcome("Hello")
+
+"Hello" is treated as the ``greet`` and we get "Hello World" as
+the output. "World" is the default value for the argument ``name``.
+
+E%% %% Pause the video here and redefine the function ``welcome``, by
+interchanging it's arguments. Place the ``name`` argument with it's
+default value of "Hello" before the ``greet`` argument. Then, resume
+the video.
+
+::
+
+ def welcome(name="World", greet):
+ print greet, name
+
+We get an error that reads ``SyntaxError: non-default argument follows
+default argument``. When defining a function all the argument with
+default values should come at the end.
+
+E%% %% Pause the video here and type ``linspace?`` to see the
+definition of the command and notice how all the arguments with
+default values are towards the end.
+
+::
+
+ linspace?
+
+E%% %% Pause the video here and redefine the function ``welcome`` with
+a default value of "Hello" to the ``greet`` argument. Then, call the
+function without any arguments. Then, resume the video.
+
+::
+
+ def welcome(greet="Hello", name="World"):
+ print greet, name
+
+
+ welcome()
+
+
+Let us now learn what keyword arguments are.
+
+{{{ show a slide with examples using keyword arguments. }}}
+::
+
+ legend(['sin(2y)'], loc = 'center')
+
+ plot(y, sin(y), 'g', linewidth = 2)
+
+ annotate('local max', xy = (1.5, 1))
+
+ pie(science.values(), labels = science.keys())
+
+When you are calling functions in Python, you don't need to remember
+the order in which to pass the arguments. Instead, you can use the
+name of the argument to pass it a value. This slide shows a few
+function calls that use keyword arguments. ``loc``, ``linewidth``,
+``xy`` and ``labels`` are being called with keyword arguments.
+
+{{{ switch to ipython terminal }}}
+
+Let us try and understand this better using the ``welcome`` function
+that we have been using all along. Let us call it in different ways
+and observe the output to see how keyword arguments work.
+
+::
+
+ welcome()
+
+ welcome("Hello", "James")
+
+ welcome("Hi", name="Guido")
+
+When no keyword is specified, the arguments are allotted based on
+their position. So, "Hi" is the value of the argument ``greet`` and
+name is passed the value "Guido".
+::
+
+ welcome(name="Guido", greet="Hey! ")
+
+When keyword arguments are used, the arguments can be called in any
+order.
+
+::
+
+ welcome(name="Guido", "Hey")
+
+This call returns an error that reads, ``non keyword arg after keyword
+arg``. Python expects all the keyword to be present towards the end.
+
+That brings us to the end of what we wanted to learn about ``keyword``
+arguments.
+
+{{{ switch to a slide showing variety of functions with uses }}}
+
+Before defining a function of your own, make sure that you check the
+standard library, for a similar function. Python is popularly called a
+"Batteries included" language, for the huge library that comes along
+with it.
+
+::
+
+ Math functions - abs, sin, ....
+
+#[punch: Need to decide, exactly what to put here. Reviewer comments
+ welcome.]
+
+
+{{{ switch to slide showing classes of functions in pylab, scipy }}}
+
+Apart from the standard library there are other libraries like ``pylab``,
+``scipy``, etc which have a huge collection of functions for scientific
+purposes.
+::
+
+ pylab
+ plot, bar, contour, boxplot, errorbar, log, polar, quiver, semilog
+
+ scipy (modules)
+ fftpack, stats, linalg, ndimage, signal, optimize, integrate
+
+{{{ switch slide to summary slide }}}
+
+That brings us to the end of this tutorial. In this tutorial we have
+learnt how to use functions with default values and keyword
+arguments. We also looked at the range of functions available in the
+Python standard library and the Scientific Computing related
+packages.
+
+Thank You!