diff -r 88a01948450d -r d33698326409 advanced_features_of_functions/script.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/advanced_features_of_functions/script.rst Wed Dec 01 16:51:35 2010 +0530 @@ -0,0 +1,277 @@ +.. Objectives +.. ---------- + +.. At the end of this tutorial, you will be able to + +.. 1. Assign default values to arguments, when defining functions +.. 2. Define and call functions with keyword arguments. +.. 3. Also, you will get a glimpse of the plethora of functions +.. available, in Python standard library and the scientific computing +.. libraries. + + +.. Prerequisites +.. ------------- + +.. 1. getting started with ipython +.. #. getting started with functions + +.. Author : Puneeth + Internal Reviewer : Anoop Jacob Thomas + External Reviewer : + Language Reviewer : Bhanukiran + Checklist OK? : [2010-10-05] + +Script +------ + +{{{ Show the slide containing title }}} + +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 and the scientific +computing libraries. + +{{{ 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. + +.. #[[Anoop: It will be good if we show ``round??`` and tell them the + optional argument ndigits, or it could be given as an + exercise(solved) asking them to find the name of the argument in + the function round]] + +{{{ show a slide with examples of functions showing default values }}} + +.. #[[Anoop: I think the slide is not there]] + +:: + + 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``. + +Following is an (are) exercise(s) that you must do. + +{{{ switch to next slide, containing problem statement of + question 1 }}} + +%%1%% Redefine the function ``welcome``, by interchanging it's +arguments. Place the ``name`` argument with it's default value of +"World" before the ``greet`` argument. + +Please, pause the video here. Do the exercise and then continue. + +{{{ switch to next slide, containing the solution to problem 1 }}} + +:: + + 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. + +.. #[[Anoop: In the slide, "when defining a function all the default + arguments must be defined at the end" has to be emphasized"]] + +Following is an exercise that you must do. + +{{{ switch to next slide, containing the problem statement of + question 2 }}} + +%%2%% See the definition of linspace using ``?`` and observe how all +the arguments with default values are towards the end. + +Please, pause the video here. Do the exercise and then continue. + +{{{ switch to next slide, containing solution to problem 2 }}} + +:: + + linspace? + +Following is an exercise that you must do. + +{{{ switch to next slide, problem statement }}} + +%%3%% Redefine the function ``welcome`` with a default value of +"Hello" to the ``greet`` argument. Then, call the function without any +arguments. + +Please, pause the video here. Do the exercise and then continue. + +{{{ switch to next slide, solution }}} + +:: + + def welcome(greet="Hello", name="World"): + print greet, name + + + welcome() + + +Let us now learn what keyword arguments or named arguments are. We +shall refer to them as keyword arguments, henceforth. + +{{{ show a slide with examples using keyword arguments. }}} + +.. #[[Anoop: slide is missing]] + +:: + + 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 }}} + +.. #[[Anoop: slide missing]] + +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 }}} + +.. #[[Anoop: slide missing]] + +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 + +{{{ Show summary slide }}} + +.. #[[Anoop: add range of functions available in python standard + library]] + +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. + +{{{ Show the "sponsored by FOSSEE" slide }}} + +This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India + +Hope you have enjoyed and found it useful. +Thank you!