RPi Education/Manual - Revision history

Antiloquax: /* Python function example */

2012-05-23T13:35:41Z

‎Python function example

Antiloquax: /* Python function example */

2012-05-23T13:33:11Z

‎Python function example

Antiloquax: /* Python Function */

2012-05-23T13:19:03Z

‎Python Function

Antiloquax: /* Python "for" Loop */

2012-05-23T13:05:16Z

‎Python "for" Loop

Antiloquax: /* Python For Loop */

2012-05-23T13:04:05Z

‎Python For Loop

Antiloquax: /* Python For Loop */

2012-05-23T12:51:34Z

‎Python For Loop

Antiloquax: /* Bash For Loop */

2012-05-23T12:51:10Z

‎Bash For Loop

Antiloquax: /* Bash For Loop */

2012-05-23T12:48:32Z

‎Bash For Loop

Antiloquax: /* C For Loop */

2012-05-23T12:33:24Z

‎C For Loop

Alecthegeek: /* Theory and tools */

2012-05-12T07:08:26Z

‎Theory and tools

@@ Line 315: / Line 315: @@
 </syntaxhighlight>
-Functions an easy way to make parts of your program re-usable. If you are going to need to do something several times in a program, it makes sense to write a function and call it each time, rather than repeating yourself. There are many advantages to this. For instance, it makes your programs shorter and if you need to change something, you only need to change it once - in the function definition.
+Functions offer a way to make parts of your program re-usable. If you are going to do something several times in a program, it makes sense to write a function and call it each time, rather than repeating yourself. There are many advantages to this. For instance, it makes your programs shorter and if you need to change something, you only need to change it once - in the function definition. In this program, the function is only called once, as it's just an example of how to do it!
-In this program we begin with "import turtle" - this tells Python that we need to use the turtle graphics features of the language. In Python (like many other languages), some features have to be loaded in this way before you can use them.
+We begin with "import turtle" - this tells Python that we need to use the turtle graphics features of the language. In Python (like many other languages), some features have to be loaded in this way before you can use them.
 Next comes the function definition. It's quite simple: "def" tells the interpreter we are defining a function and the next word will be its name ("polygon"). In Python, all functions have brackets following their names (for instance "print()" is a function). You can make a function that doesn't need anything inside those brackets, but this one takes two arguments. In this case, it is the number of sides and the length of the sides. After the definition, we use a colon and indent the following block of code.
@@ Line 323: / Line 323: @@
 Our function consists of a simple loop that makes the "turtle" move forward the required distance (in pixels) and turns through the appropriate angle (360 degrees divided by the number of sides).
-After the definition of the function, there's a comment that now we are in the main part of the program. The function won't do anything until it is called. The next lines are fairly simple and just get some values from the user. You'll notice that the names of these variables are different from the ones I used in my function definition. You could use the same names, but it will be less confusing if you do it this way, the function will store temporary copies of the values in its own "length" and "sides" variables. We call the function just like any other, with the name of the function and the arguments in brackets, separated by a comma. Once the function is complete, it will return control to the main part of the program - which just asks us to press enter.
+After the definition of the function, there's a comment that now we are in the main part of the program. The function won't do anything until it is called. The next lines are fairly simple and just get some values from the user. You'll notice that the names of these variables are different from the ones used in the function definition. You could use the same names, but it will be less confusing if you do it this way; the function will store temporary copies of the data in its own "length" and "sides" variables. We call the function just like any other, with the name of the function and the arguments in brackets, separated by a comma. Once the function is complete, it will return control to the main part of the program - which just asks us to press enter.

@@ Line 312: / Line 312: @@
 how_big = int(input("How long do you want the sides?"))
 polygon(how_big, how_many)
-input("Press a key to quit.")
+input("Press enter to quit.")
 </syntaxhighlight>
@@ Line 319: / Line 319: @@
 In this program we begin with "import turtle" - this tells Python that we need to use the turtle graphics features of the language. In Python (like many other languages), some features have to be loaded in this way before you can use them.
-Next comes the function definition. It's quite simple: "def" tells the interpreter we are defining a function and the next word will be its name ("polygon"). Function definitions require
+Next comes the function definition. It's quite simple: "def" tells the interpreter we are defining a function and the next word will be its name ("polygon"). In Python, all functions have brackets following their names (for instance "print()" is a function). You can make a function that doesn't need anything inside those brackets, but this one takes two arguments. In this case, it is the number of sides and the length of the sides. After the definition, we use a colon and indent the following block of code.
 ===objects===

@@ Line 295: / Line 295: @@
 ===functions===
 reusable blocks of code
 ===objects===

@@ Line 262: / Line 262: @@
 The lines that begin with "#" are comments. They are ignored when the program is run, but help to make your code readable by humans.
-In the "for" command we state that we are using the variable "i" as the counter in the loop. The section in brackets defines the start and end points, as well as the steps. Here, we are starting at 10 and going down to 0. (Although the last number we see will be one - when the loop hits 0 it will continue to the next instruction. The "-1" means we are counting down by one each time. The "for" line ends with a colon - this is important. The colon, together with the indentation, makes it clear to the Python interpreter that the block of code following is to be run each time through the loop. In Python, each level of indentation should be one tab or 4 spaces. You can use either, but not a mixture of both.
+In the "for" command we state that we are using the variable "i" as the counter in the loop. The section in brackets defines the start and end points, as well as the steps. Here, we are starting at 10 and going down to 0. (Although the last number we see will be one - when the loop hits 0 it will continue to the next instruction). The "-1" means we are counting down by one each time. The "for" line ends with a colon - this is important. The colon, together with the indentation, makes it clear to the Python interpreter that the block of code following is to be run each time through the loop. In Python, each level of indentation should be one tab or 4 spaces. You can use either, but not a mixture of both.
 Inside the loop, we have a simple print statement. First, "Looping: " is printed and then the current value of "i".

@@ Line 247: / Line 247: @@
 </syntaxhighlight>
-== Python For Loop ==
+== Python "for" Loop ==
 This is an example of a simple "for" loop in Python.
@@ Line 267: / Line 267: @@
 The final line is not indented, and therefore is not part of the loop. This simply prints: "Done" once the loop has completed.

@@ Line 246: / Line 246: @@
 done
 </syntaxhighlight>
 ===operators===

@@ Line 186: / Line 186: @@
 *Next copy and past the code below into the text editor. This can be done by right clicking your mouse and clicking copy, then in the text editor right click your mouse and select paste. ('''HINT: in gedit you can enable syntax highlighting, which will make the important parts of the code coloured like in the example below.''')
 *Now you need to save the code. In gedit click on file and save, a save window will then appear. Choose a name for your file, I suggest loop.c, but any name is fine so long it has a ".c" after it, and save it in the Documents folder. If you are using nano press and hold the control (ctrl) key on your keyboard and then press the 'x' key. There will be some text asking you to save the code before you exit type 'y' and press enter. Then type in loop.c and press enter. This has now saved your file as loop.c.
-*Now if you used type "gcc -o loop loop.c" replaceing loop.c with whatever you called you code file. This should finish quite quickly and no text should appear. If any errors appear check what you have typed into your code file very carefully and make sure that it is exactly like the one in the example.
+*Now if you used type "gcc -o loop loop.c" replacing loop.c with whatever you called you code file. This should finish quite quickly and no text should appear. If any errors appear check what you have typed into your code file very carefully and make sure that it is exactly like the one in the example.
 *You should now have a new file in your documents folder called "loop", you can check this by typeing "ls" then press enter to display a list of files in you documents folder.
 *To run the program you need to type "./loop" and press enter. The program should now have the output:
@@ Line 196: / Line 196: @@
 int main(void)
+{
-    int counter;    // Initialise the counter variable.
+    int count;    // Initialise the counter variable.
     for(count = 0; count < 10; count++)
@@ Line 212: / Line 212: @@
 Scopes in C are indicated by curly braces '{' to start and '}' to finish. In the case of the main function in this program a "return 0;" statement is positioned at the end of a function. This lets the computer know that when the program finishes that everything ran properly.</p>
-The next statement "int counter;" tells the computer to create a variable called counter. Variables are used to store data such as numbers or sentences. In C variables should be created or "declared" at the beginning of a function, this is not completly nessesary as newer C compilers often allow you to ignore this rule. However it is recomended to stick to it, as when you are trying to find out why your program is not working it will be easier to see which variables are local to, in other words in the function and which variables are global to the program, or outside your function, but not in another function.
+The next statement "int count;" tells the computer to create a variable called count. Variables are used to store data such as numbers or sentences. In C variables should be created or "declared" at the beginning of a function, this is not completly nessesary as newer C compilers often allow you to ignore this rule. However it is recomended to stick to it, as when you are trying to find out why your program is not working it will be easier to see which variables are local to, in other words in the function and which variables are global to the program, or outside your function, but not in another function.
 Next the loop is started. The for statement indicates that the loop is a "for" loop. The next part surrounded in brackets "()" is a small bit of code telling the for loop how many times it should run. The fist bit "count = 0" sets the counter to 0 this is followed by a semicolon then the statement "count < 10" this meens that the code in the for loop should be repeated while the value of "count" is less than 10. This is followed by another semicolon and the statement count++. This part is run every time the for loop reaches the end. In this case the for loop increments, or increases, the value stored in count by 1. This could be replaced by "count = count + 1" if you wanted to and it would do the same thing.

@@ Line 277: / Line 277: @@
 ==Theory and tools==
-* [[Version Control]]: git, <del>svn</del>, bzr, hg etc
+* [[Version Control]]: Concepts, git, <del>svn, bzr, hg</del> etc
 * Iterative and Test Driven Development
 * Writing software for someone else (User Stories, Use Cases, requirements, contracts)