csci133c3.py

Welcome to the 3rd notes for the python programming lab. Let's take a look at the code and see what does it do. Today we will talk about the function. Function is a block of code that do varies kind of thing, and might or might not return the value it get.

line = 'This is a sample line of text.'
# Measure the length of the line string
print(len(line))

# Split the line string by spaces, return a list
print(line.split())

# Measure how many word are there now
print(len(line.split()))

Output:

30
['This', 'is', 'a', 'sample', 'line', 'of', 'text.']
7

Pay close attention to line #3, when we call a function (or to use a function). We can also pass some data if the function accept it, that data is called parameter, or argument. So we passed the line into the length function, len(line). And the function returned the result of 30, and then it is being passed to the print function and print on the screen. That is why it is outputed as 30.

Whenever we want to print thing on the screen, we are always actually calling the print function, and passing the number, letter, or word into the function. What about the split function? What does it do? From the python's web manual.
http://docs.python.org/library/stdtypes.html#str.split

str.split([sep[, maxsplit]])

Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit is not specified, then there is no limit on the number of splits (all possible splits are made).

For example, ' 1 2 3 '.split() returns ['1', '2', '3'], and ' 1 2 3 '.split(None, 1) returns ['1', '2 3 '].

The function require a string to be invoked on, that's why it has str.split(), the split function actually takes argument. But at the moment we just want it to split with blanks, or spaces. Note each data type has their own set of functions build in to them.

Example Problem #1: Turn a string into all lower case
If you want to turn a string to lower case

word = 'THE QUEEN'
word = 'THE APPLE'
newWord = word.lower()
print('Before:', word)
print('After:', newWord)

Output:

Before: THE QUEEN
After: the queen

Example Problem #2: Turn every word into lower case, remove the symbols, print them one by one. (One on each line). String is from a random novel on the web.

line = 'http://www.gutenberg.org/cache/epub/39133/pg39133.txt'
newLine = ''
for char in line:
    if char in 'abcdefghijklmnopqrstuvwxyz':
        newLine = newLine + char
    else:
        newLine = newLine + ' '
print('Before:', line)
print('After:', newLine)
print('Split it:', newLine.split())
for word in newLine.split():
    print(word)

Output:

Before: http://www.gutenberg.org/cache/epub/39133/pg39133.txt
After: http   www gutenberg org cache epub       pg      txt
Split it: ['http', 'www', 'gutenberg', 'org', 'cache', 'epub', 'pg', 'txt']
http
www
gutenberg
org
cache
epub
pg
txt 

So before we go, let's go to this link, download the file into our current dir. Because the next tutorial we will use that file! http://www.gutenberg.org/cache/epub/39133/pg39133.txt , and rename it to book.txt

Practice Problem:  Write a program to clean up the following string, turn all letters into lower case, and print one word per line.

foo = '[_He approaches Fabiani._]'

Output:

he
approaches
fabiani

Pydev in Eclipse on Mac

When you downloaded Pydev for Eclipse, you have to set up the Python interpreter before you can start using it. Here is the instruction.

To configure a Python or Jython interpreter in 
Eclipse > Preferences > PyDev



When you are in Preferences, find PyDev, and click on the Interpreter - Python



Choose New in the upper right and enter /usr/bin/python
Eclipse will then take care of the rest for you – ie. updating the $PYTHONPATH

Reference & Credit: On Using Pydev on a Mac.

Python Reference Link

In this post I will include all the reference I used when I am learning Python, some of them are textbook, some of them are website.

• http://effbot.org/tkinterbook/tkinter-whats-tkinter.htm
  Very easy and simple to read, proivde a good starting point if you never done any kind of GUI before. It is very short and to the point, there are no complicated theory or other information. Not to say it is not important however, but to get you up to speed and start writing software, it is great!
• http://stackoverflow.com/questions/tagged/python
  A google for programming related question, actually it is a really good idea to just read the questions and the answers. Sometimes it is like little trick and tips, sometimes it is the concept explained in another point of view that is not like from a textbook, but from a working professional programmer. It fits the bill of learning something everyday ;)
• http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html
  It is like a python programming guide with a lot of cool tips and trick that a new programmers might overlook. Good read, and interesting.
• http://docs.python.org/tutorial/
  The best tutorial there is for beginner learning how to write program in python. It talks about a lot of the buildin function, type, module. It shows great example code as well as the required parameters and return type.

Python's Doc Tutorial Notes

Chapter 1: Whetting Your Appetite

Python is really simple to use, but at the same time it offer more structure and support for large program. In particular, the error checking is very well developed compare to C. Where in C, they expect you to make judgement yourself, and handle the possible problem yourself. And of course, Python has a lot of high-level data types built in, such as flexible array and dictionaries, which can be apply to all types, even your own class. Similar to C++'s vector, you can put your class object into the vector.

Python follows the main heart idea of OOP, it allows user to separate and export their program into modules. And then you can reuse or extend it as needed. There are quite a few module that comes standard with all the python installation, such as file I/O, system calls, sockets, and graphical user interface toolkit such as tkinter.

Python is an interpreted language, so you don't have to worry about comilating and linking your file. Remember when you write a c program, instead of just pressing a "run" button, or F5 in the default IDE, you will instead go to your terminal, type in: g++ -Wall -o csci133p1 csci133p1.cpp ccsci133myClass.cpp. These sort of goodies, after you type them, and then you are hit with a wall of error message that is not very human-readable, but except telling you line number x is broken?

And a couple of key note-worthy characteristic:

1. Python can do complex operations in 1 liner, and in fact most python programmer love the 1 liner solutions a lot.
2. Python's statement grouping is done by indentation, instead of the ending brackets {}
3. There are no variable type declaration, and similarly, there is no return type specified. You can return as many things as your heart desire, by doing return my_number, my_home, my_food

Python's name has nothing to do with the reptiles, it is because the author like the BBC show "Monty Python's Flying Cirus". But despite reading this, I still think about python as "a big snake". :)

Chapter 2.1 Notes

csci133c2.py

After we learn how to write a loop, we can do more by combining two or more of them. It is actually very easy too. Say I want to list all the possible combination of ice cream. I want to create something that will output this.

# Output desired
I like Vanilla ice cream with Gummy Bear
I like Vanilla ice cream with Cookies
I like Vanilla ice cream with Nuts
I like Vanilla ice cream with Chips
I like Chocolate ice cream with Gummy Bear
I like Chocolate ice cream with Cookies
I like Chocolate ice cream with Nuts
I like Chocolate ice cream with Chips

There are 2 kinds of ice cream and 4 kinds of topping in this program, so we most likely going to need 2 list, and then we loop them each through another.

# Solution code for the example above
iceCreams = ['Vanilla', 'Chocolate']
toppings = ['Gummy Bear', 'Cookies', 'Nuts', 'Chips']
# Looping through the ice creams
for iceCream in iceCreams:
    # Looping through the toppings
    for topping in toppings:
        print('I like', iceCream, 'ice cream with', topping)

There you have it, it is actually very simply to check for all possible combinations of the items you have in your list, does not matter if they are food, student, car, dog, anything you want. Anyway, so now let say you only want Cookies as your topping on your ice cream, you will need to check if topping is cookies, here is how to do it in python!

# if statement example
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
prime = [1, 2, 3, 5, 7]
for number in numbers:
    # Check if the number is in the list of prime we have
    if number in prime:
       print('The number', number, 'is a prime!')

Output:

The number 1 is a prime!
The number 2 is a prime!
The number 3 is a prime!
The number 5 is a prime!
The number 7 is a prime!

Note, this is just an example to showcase the example of the if statement, in real life this is not how it is done. A much more useful example: The vowels example:

# Example problem that check for vowels
vowels = 'aeiou'
words = ['apple', 'banana', 'orange', 'grapes', 'mango']
for word in words:
    for letter in word:
            if letter in vowels:
               print(letter, 'is in the word:', word)

Output:

a is in the word: apple
e is in the word: apple
a is in the word: banana
a is in the word: banana
a is in the word: banana
o is in the word: orange
a is in the word: orange
e is in the word: orange
a is in the word: grapes
e is in the word: grapes
a is in the word: mango
o is in the word: mango

Practice Problem:
Write a program that checks the word 'google', and print what are the vowels.
Write a program that print one type of ice cream on each line

# Use this list of ice cream for the practice problem
iceCreams = ['Vanilla', 'Chocolate', 'Strawberry',
             'Neapolitan', 'Chocolate Chip', 'French vanilla', 
             'Cookies and Cream', 'Vanilla Fudge Ripple', 'Praline pecan']

Write a program that print 'I love ice cream' 50 times :)

# Tip: Don't write print() 16 times, think about loop, n * n = 16...?

Write a program that count down from 20 to 1

# Tip: Create an integer counter, and -1 each time you run through
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1

Write a program that check the vowel in the ice cream name list

# Use this list of ice cream for the practice problem
iceCreams = ['Vanilla', 'Chocolate']

Solution

# Solution on the question
iceCreams = ['Vanilla', 'Chocolate']
vowels = 'aeiou'
for iceCream in iceCreams:
    for letter in iceCream:
        for letter in vowels:
            print(iceCream, 'has vowel', letter, 'in it')

csci133c1.py

In the first program we are going to start with "Hello World", in python it is actually really simple to do. Type the below code into the file, and press save and run!

# Example: Hello World
print('Hello World! Python is fun!')

Output:

Hello World! Python is fun!

Notice in the single quote signs, what is between ' ' is viewed as a sequence of characters. Unlike in C++, python is an interrupt language, we don't need to complie, we just need to save and run it. (Control + Save) Then (F5) And in python, you can comment with " # " sign, the python will not do anything to that line, it is for reference and notes. It is always good habit to document your code, and keep the comments outdated when you make changes.

Let's create a string variable name food, and we print "I like that food".

# Example: Printing with variable
food = 'cookies'
print('I like', food)

Output:

I like cookies

Here there we learn two things, one is the way the python declare the variable, without a type. It takes care of figuring out what is the type, base on what you give it. In this case the food is a string variable, and the way to include the variable in the print, we separate it with a comma (,).  And let's take a closer look at the first line, the equal sign does not mean food is equal to cookies, rather it mean we assign cookies to the object data named food. There is a difference there, it would be best if we read it as, "food is the name of the string for cookies", or "cookie is now food" in our program. Below is another example to demonstrate how to use a few variable at the time in the print.

# Example: What do you eat everyday?
breakfast = 'milk'
lunch = 'burger'
dinner = 'steak'
print('I eat', breakfast, lunch, dinner, 'everyday.')

Output:

I eat milk, burger, steak everyday.

This example we can see we can chain more variables in the print statement, you can do it with different variables if you have other. And take a note on the following piece of example, guess what is the output?

# Little Quiz 
breakfast = egg
print('Today"'"s breakfast:', breakfast
breakfast = sandwich
print('Today"'"s breakfast:', breakfast

Can you guess what is the output?
Here is the answer!

Today's breakfast: egg
Today's breakfast: sandwich

If you guessed correctly, good job! And if you wonder why I used double quotes ( " ), it is because it is the only way to print single quote. You need to wrap the single quote in a double quotes. "'". Try it and see if it works!

But it is kind of hard to type out all this, if we have many many different kind of food for breakfast, what if we have 5 different foods, do we need to write 5 identical print lines? The answer is no! Check out the following example.

# Simple for loop example
foods = ['egg', 'juice', 'apple', 'bread', 'cookies']
for food in foods:
    print('Today"'"s breakfast:', food)

Output

Today's breakfast: egg
Today's breakfast: juice
Today's breakfast: apple
Today's breakfast: bread
Today's breakfast: cookies

Don't you think it is a lot easier this way? And feel free to type your own favorite food for breakfast. For these who are new to python programming, there is actually a lot going on in this example.

1. The object we created in the example above is a list, in this case it is a list contain 5 string objects, a list is a sequence of objects. We create list in python by separating the string objects with commas, and enclose the sequence with square brackets. Another example of a list contain 2 student: ['Sam', 'Kelly']
   
2. You can create a list of other types too, with integers, whole numbers, such as 1, 2, 3, 4, 5, including negative numbers too. Example: dates = [1, 5, 12, 19, 20]. We have here a list object name dates, containing 5 integers.
   
3. There is control statement, or as call it, a for loop. The structure of the statement is like this:
   

   # Example for a for loop control statement
   for object in objects:
   <Indentation> statement
   <Indentation> statement

   The python only know the statement is "inside" a loop when you indent it, otherwise it has no way of knowing. It is different from say other language like C++, as they use {} to create a block of code. And although we don't have to end every single statement with " ; ", but in the case for the loop, we need to add a colon " : ", to let python know this is the end of the condition. I provide readers with a few more example here:
   

   # Always object for object(s)
   for line in lines:
   <Indentation> statement
   
   for car in cars:
   <Indentation> statement
   
   for class in classes:
   <Indentation> statement 

However, python doesn't care what name we use, just like in other programming language, the name (identifier) is for the programmers (human) to read. So there is nothing stopping you to do something silly like this.

# A really bad example
aawhjwb = [1, 5, 20, 55]
for bbb in aawhjwb:
    print('Visit doctor at: ', bbb, 'of this month')

But it will be very hard to remember what is going on, so try to use something that make sense, that way it is easier to debug and for other programmers to read your code. Please do not do not do this.

Practice Problem:
Write a program that produce the following output:
Tip: Create a list contain 3 student's name.

Hello George
Hello Peter
Hello Joe

Write a program that produce the following output:
Tip: To print an empty line, do print(), this will produce an empty line

Red Car
Red Truck
Red Tank
Red Boat

Blue Car
Blue Truck
Blue Tank 
Blue Boat

Green Car
Green Truck
Green Tank
Green Boat

csci133Tkinter.py

A post about Tkinter's most common usage question, answer and demonstration sample code.

csci133string.py

Reference: http://docs.python.org/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange

String is one of the most if not the most common object used in all languages, you can create a string object by doing.

myString = 'George'

# Work in progress #

csci135c3.cpp

This is the second kind of loops, the while loops. In this tutorial, I am also going to demonstrate a variation of the while loop, the do-while loop.

/*
 *  csci135c3.cpp
 *  This program shows the useage of the while loop.
 *
 */

#include <iostream>
using namespace std;

int main()
{
   int counter = 5; // our integer counter variable
   cout << "While loop #1, while counter > 0" << endl;
   while (counter > 0)
   {
      cout << "Counter is now: " << counter << endl;
      counter--;
   }
   
   counter = 10; // reset counter back to 10
   cout << endl; // just for the display, this skip one line 
   
   cout << "Do While loop, while counter > 0" << endl;
   do
   {
      cout << "It still run one time although it does not satisific the "
      << "condition counter > 10 " << endl;
      counter--;
   } while (counter > 10);
   
   return 0;
}

The format of the loop is like this:

while (condition)
{
   // do something here
   // some kind of counter adjustment
}

The concept of the while loop is just like how it sounds, while condition is true, do the execution in the block. But unlike the for loop, the counter adjusting is do in the loop. See the example, line 17 is counter--. Of course, you can increment as well. At this point, you might be asking: “What happen if we do not know in advance how many times we need to run?” This is not true, because we can use variable in the condition. You can do something like this.

while (counter > whereToStop)
{
   // do something here
}

However, something important need to be clear. Be careful that your loop, whether it is a for loop or while loop, it is not an infinite loop. An infinite loop is a loop that will not terminate, something it is because the condition is always possible to satisfy, or more frequently, remember to include the counter adjustment. Below are some examples that show what possible mistake one can make.
int counter = 0;

while (counter < 10)
{
   // No decrement or increment, it won't be ever greater than or equal
   // to 10. So it will be an infinite loop.
}

int counter = 10;
while (counter > 10)
{
   // the counter is going the opposite direction, and it will
   // never be greater than 10. This is an infinite loop.
   counter--;
}

Lastly, there are times when you do want the loop be infinite. I remember it the canvas GUI program, the screen requires to be refreshed until the user click the close button. You do not need to use the above examples, you can simply do the follow.

while (true)
{
   // do something here
}

This is a very well know way to create an infinite loop, all the programmers understand this is a loop that wanted to be run forever. There are some usage of this, just take know of such a thing.

Finally, let’s look at the do while loop at the last part. This loop is interesting because, even though the condition of the loop does not satisfy, it will still run for the first time. Let me give you a real world example, let say everyone can get a free cookies from the school’s café, and you can get more if you have a ticket, each ticket you have allow you to get one more cookie. So everyone get to the school café, the loop in this case, will get to run once.

int ticket = 5; // the amount of cookie tickets they have
do 
{
   cout << "Give you a piece of cookie. " << endl;
   ticket--;
} while (ticket >= 0);

Note, this case the student will get 6 pieces of cookies. The first one that everybody gets just by showing up, and then 5 more cookies (from the exchange of tickets). There are many situations too, this is just one of the example I come up with. And plus who doesn’t like cookie? :9
Note: This example has some problems, edit or remove before publish. 

Practice Problem

Write a program that will count from 0 to 10. The output should be like the following.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

csci135c2.cpp

A program is good for doing things thousands of times and accurately. What if we want repeat doing something many times? How should we program this? It is okay for us to type it out line by line if the number is small, but what if we want to write from 1 to 1000? We need some kind of looping function to do this!

/*
 *  csci135c2a.cpp
 *  This program count from 1-20, by hand, typing it out one by one. It might
 *  taking a little bit longer time than using a loop. But let's try it out.
 *
 */

#include <iostream>
using namespace std;

int main()
{
    cout << "1 " << "2 " << "3 " << "4 " << "5 " << "6 " << "7 " << "8 " << "9 " 
         << "10 " << "11 " << "12 " << "13 " << "14 " << "15 " << "16 " << "17 " 
         << "18 " << "19 " << "20 " << endl;
    cout << "I am tired, we need to write a loop to do this." << endl;
    return 0;
}

Not only this takes a lot of time to write, but the size of this program is also much larger than what it will take if it is written in a loop. Now let's look at how to do it with a for loop, it require much less typing, and the chances of making a typo error is also much smaller. Remember what does int mean? (answer, int means integer, 0,1,2,3)

/*
 *  csci135c2a.cpp
 *  This is the for loop version of the previous program, this is much easier
 *  to write a loop that count a few thousands time. Rather than writing it 
 *  line by line by hand. Just need to change the int i = x part.
 *
 */

#include <iostream>
using namespace std;

int main()
{
   // this the for loop, that count from 0 = 20, i+1 is the offset, because
   // this count from 0-19. But we want to print from 1-20, so offset is 1
   for (int i = 0; i <= 20; i++){
      cout << i+1;
   }
   cout << endl; // this is the space to skip to the next line
   cout << "I am tired, we need to write a loop to do this." << endl;
   return 0;
}

First we take a look at the structure of a "for" loop:

for (set up counter; condition of the counter; counter adjustment){
   // do something here
}

In pain English, this can be view as the following: "for an integer start at 0, i is less or equal to 20, i plus plus. Then in the loop we can print the value of i (offset is 1 in this case)." Usually (for general usage), the counter will be an int, and it can be named anything you like. But a single letter i, j, k, will more popular, because it is also used as index for array and vector. But nothing is wrong with a name called "counter" too, the condition of the counter, there are many examples. i < 10, means it goes up to 9. i <= 10, means it goes to 10. As for the adjustment, you can let the counter count up to 10, or count down to 10. Both is correct usage depend on what you do, there is no right or wrong answer here.

// Increment from 0 to 9 (total of 10 times)
for (int i = 0;  i <= 10; i++)
{
   // do something here
}

// Decrement from 10 - 0 (total of 10 times)
for (int i = 10; i <= 0; i--)
{
   // do something here
}

This two function will both execute the statement within 10 times. But to be sure, if you want to print out from 0-10, you need to do some adjustment to the decrement version. Because the counter i is going from 10 to 1, and if you want to print from 1 to 10, then you can do the following.

// Print 0 to 10 in the decrementing fashion of for loop
for (int i = 10; i <= 1; i--)
{
   int number = 0; // declare a integer variable for displaying our value
   cout << number << endl;
   number++; // increment the printing number
}

Practice Problem:
Write a program that display the first 10 odd number using the for loop, they should be in the same format as below. Separated by a comma. Tips: You can use the offset to display the odd number, try different offset and see what happen.

1, 3, 5, 7, 9, 11, 13, 15, 17, 19