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Python Scratch is great for learning the basics of programming, but sooner or later you're going to run into its limitations. Now we're going to take a look at a popular general-purpose language, Python. The first thing you need to know about Python is that, unlike Scratch, it's entirely text-based. This doesn't mean that it can't create graphics, but that the program code is text rather than drag-and-drop blocks. Your Pi ships with IDLE – a Python development environment – that allows you to input commands. It includes a handy help command that can help you with your syntax, and also comes with its own built-in text editor, with colour-coded syntax and automatic placing of indents, to help with your programming. Note: because Python's code is text based, you can use any text editor to create a program – Leafpad comes with the Pi, for example.
Geany is another popular choice with new Python programmers. Avoid the use of word processors such as LibreOffice Writer, however, because they mess up the formatting and prevent your program from functioning correctly. Okay, open the Pi menu and choose Programming Python 3. This is the command line, but we want IDLE's text editor, so choose File New to create a new blank document. On the first line, add: #!/usr/bin/python This line, rather cryptically called a 'shebang', tells the system to use the program python, in the folder /usr/bin/ to run the file. You'll need to add it to the start of all your Python programs.
We can now get onto the guts of programming. There's a long-standing computing tradition of having your first program output 'Hello World!' , and we're not going to break it here. Leave the second line blank (not strictly necessary, but it makes your code easier to read), and on the third type: print 'Hello World!' And save your work in a file called hello.py. To run the program, you need to open a terminal and navigate to where you saved the file (your home folder by default).
First, type the following command to tell the system the file is executable: $ chmod a+x hello.py Next, type this command to run your program: $./hello.py You should see Hello World! Appear on the screen.
This shows us that the system is running properly, but it's not a very useful program. As with the Scratch project, we'll add some user input. However, with Python we'll need to add a variable to store what the user types. Delete the Hello World line (leaving just the shebang), and add the line: name = rawinput('what is your name? ') This line creates the variable name, displays the prompt 'What is your name? ', and stores what the user types in name. We have to enclose this in inverted commas so that the computer knows it's a single chunk of text.
We can then use this variable to make our print statement a little more personal with the line: print 'Hello', name Since the computer will run the commands in order, this one needs to be below the previous one. If they are the other way round, the program will throw up an error because we are using a variable before we have created it. You can now save the file, and enter./hello.py at the command line to run the program. Decisions decisions This makes the program a little more functional, but it's still pretty lifeless. It just follows the same two steps, then finishes. To make it useful, we need to add a decision step, where the computer looks at the input, and performs different actions depending on what it finds. Remember the If block in Scratch?
Well, we can use the same thing here. The basic structure of the block is: if: code block must be replaced with anything that can be true or false. For example, 1 2, or more usefully, num 2 where num is a variable. In our case, we'll check if the name entered is a particular value: if name 'Ben': Why ?
Well, computers (and programmers for that matter) don't deal well with ambiguity. Each symbol or word we use should have precisely one meaning, otherwise things get confusing. = is used to assign a value to a variable, so we need to use something else to check equality. Again, we have to enclose Ben in inverted commas so the computer knows it's text. The colon tells it that we've finished our expression and we're about to tell it what to do. We may want this If command to run more than one line of code, so we need a way to group code into blocks. In Python, this is done using indents (Python is more-or-less unique in this respect, and this method is a bone of contention to Python-haters).
Indents can be a space or a tab, but it's really important that you always use the same throughout your project, otherwise it can get horribly confusing, since it doesn't go on the amount of indentation, but the number of indents. Personally, we recommend using two spaces for each indent, because that's the way we were taught, and we're too stubborn to change – IDLE attempts to insert these automatically for you. So, what do we want the computer to do if name 'Ben'? Well, obviously, we want it to greet him in the appropriate manner: if name 'Ben': print 'Ben, you're awesome' Note the two spaces at the start of the second line. Note how we use double speech marks. This is because the text we're enclosing has an apostrophe in it. We don't want to be rude to other people, so we'll add an else block that runs whenever the if expression is false: else: print 'Hello', name One last feature we'll add to our program is a loop.
This will work much like the one we added to our Scratch program, except that it won't only run 24 times, it'll keep running until we tell it to stop. We do this using a while loop and the syntax: while: code block We can tell the program to stop by entering the name quit. So, our while loop will be: while name!= 'quit': Solving problems Don't ask us why, but exclamation marks are often used to mean not in programming. But this still leaves us with a bit of a problem. If we put it before name = rawinput then it will produce an error, saying it doesn't know what name is. If we put it after, it will only ask us to enter a name once, then keep spitting out its greeting indefinitely. To solve this, we can simply assign the empty string to name before while.
This stops it erroring, and will always trigger the while expression. So, our little program now looks like this: #!/usr/bin/python name = ' while name!= 'quit': name = rawinput('What is your name? ') if name 'Ben': print 'Ben, you're awesome' else: print 'Hello', name Note the four spaces before each print line. This is because they're indented twice – once for the whileloop and once for the if statement.
You can save this as hello.py, as before, and run it with./hello.py. Where to go now? If you've followed this tutorial and enjoyed writing your first programs, then you may be wondering what to do next. Well, both Scratch and Python are great languages to get started with, so first you have to pick the one that appealed the most to you. If it was Scratch, the best place to start is. Here, you'll find loads of projects that other people have done that you can take a look at, along with video tutorials and tours to help you learn the environment.
Python is a far more popular language in the real world, so you'll find many more resources to help you learn. The has a tutorial, which explains the language well, but can be a bit dry. There are a number of excellent books on the subject (such as Dive into Python, which can been read for free at ). Subscribers to Linux Format can access more Python tutorials via the archives at, where you'll also find our Code Concepts series, which helps introduce the key ideas behind programming.
This project has been excerpted and modified from. What You’ll Be Making You’ll create a very simple counting program using Python. Python is considered an “interpreted language,” which means that you can write a program or script and execute it directly rather than compiling it into machine code. Interpreted languages are a bit quicker to program with, and Python comes with a few side benefits of its own. For example, in Python you don’t have to explicitly tell the computer whether a variable is a number, a list, or a string; the interpreter figures out the data types when you execute the script.
The Python interpreter can be run in two ways: as an interactive shell to execute individual commands, or as a command-line program to execute standalone scripts. The integrated development environment (IDE) bundled with Python and the Raspberry Pi is called IDLE.
You’ll learn the basics of Python through this mini project. If you aren’t familiar with what a shell is, it is a user interface for accessing an operating system’s services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer’s role and particular operation. What You’ll Learn. The basics of Python, a programming language. How to put chunks of code into functions for easy re-use.
Working with variables and loops. The best way to start learning Python is to jump right in. Although you can use any text editor to start scripting, we’ll start out using the IDE. Open up the IDLE 3 application. To run IDLE, double-click the IDLE 3 icon on the desktop, or click the desktop menu in the lower left, and choose Programming→IDLE 3.
IDLE can take several seconds to start up, but when it appears, you’ll see a window with the interactive shell (Image on left). The triple chevron is the interactive prompt; when you see the prompt, it means the interpreter is waiting for your commands.
To start a new Python program, select File→New Window, and IDLE will give you a script editing window (Image on right). If you’re coming to Python from the Arduino world, you’re used to writing programs (known as sketches in Arduino, but often called scripts in Python) in a setup/loop format, where setup is a function run once and loop is a function that executes over and over. The following example shows how to achieve this in Python. With the script editing window you opened in the previous step, type the code in the first image. It may not be obvious that each level of indentation is four spaces, not a tab (but you can press tab in IDLE and it will dutifully insert spaces for you). It’s important to watch your whitespace. Python is a highly structured language where the whitespace determines the structure.
This differs from languages like C that delimit blocks of code with brackets or other markers. To run your program, select Run Module and give your script a name (such as EvenIntegers.py). As it runs, you should see all even integers printed (press Ctrl-C to interrupt the output, because it will go on forever!). You can change this program to create a loop that just counts the first 100 even integers. Add the code in Image 2 to the bottom of your code. Now, we’re going to use functions to put chunks of code into a code block that can be invoked from other places in your script.
To rewrite your program with functions, type the code in Image 1. Note: Everything indented one level below the loop function is considered part of that function.
The end of a loop is determined by where the indentation moves up a level (or end of the file). Run your code and save it as CountEvens.py. Based on the code you’ve written, the output will be every even number from 102 on. Here’s how it works (reference the numbers above). The variable n is defined as a global variable that can be used in any block in the script. The setup function is defined (but not yet executed).
Similarly, the loop function is defined. In the main code block, the setup function is called once, then the loop function is called. The use of the global keyword in the first line of each function is important; it tells the interpreter to use the global variable n rather than create a second n variable that can only be used in the function.
Code: #!/bin/sh # #Front end for GCC compiler. Hello, I have started working on RPi two days ago.
I have seen some tutorials to program RPi using Python but I do not have any experience in Python. I am very good at C. I do not have time to learn Python because I want to finish my project as soon as possible.
I want to read the sensors using I2C. I have a 4 channel board to connect the sensors with the board. Is it possible to read the sensors using C language only?
Please help me if somebody has experience to read the GPIO of RPi using C. Waiting for you valuable comments. You were asking which text editor to use so I'll write out every step which works from the prompt on a default raspian wheezy installation and also works in a terminal after startx has been called. Cd where brackets indicate something which you must change to what you are using. Nano helloworld.c opens a blank helloworld.c in one of the text editors type in some c code to do something, preferably not printf-ing any rude words.
CTRL-O to save CTRL-X to exit that will return you to the prompt, where you may type gcc -o helloworld hellowold.c ls -l to list what is there with details. Chmod +x helloworld if ls-l did not find an 'x' for 'executable' against helloworld note that executables might sometimes be coloured green to make them more noticeable from ls. To run an executable named helloworld./helloworld what happens next will be whatever was asked for correctly in your program. Thanks but it does not answer my question. Crack para textaloud 3.0.29. I assume I open the terminal under Accessories then type cc -o cprog myprog.c where is the Pi expecting to find the directory cprog? Should I have saved it in Home or Home Pi or somewhere else?
No place seems to work. Where is the 'command line'?
Does this mean the Terminal? What does -o mean? Or is that a zero?
I also assume that cc invokes a C compiler but which one? Is there even one loaded?
I read the guide and RPi Basics but need some other reference to cover these basic steps. The last post helps with the -o thanks. Is this stuff I don't understand a Linux thing?
Programs For Raspberry Pi
It is totally strange to me.
Writing Programs On Pc For Raspberry Pi
In this tutorial, I’ll discuss what the C programming language is, what C programming is used for, and how to write and run a C program on the Raspberry Pi. The intent of this article is to give you a very basic introduction to C programming on the Raspberry Pi. If you’re looking for more in-depth information on C programming, a great book to have is. It’s a useful reference for both experienced programmers and anyone that wants to learn the C language. What is a C Program? The C programming language is one of the most widely used programming languages of all time.
Programs written in C can be run on a wide range of platforms including personal computers, embedded microcontrollers, and supercomputers. One advantage of C is that the code runs almost as fast as assembly code. Like assembly code, C lets you access powerful low level machine functions, and it has a syntax that is easier to read than assembly code. For example, compare this assembly code for a “hello world” program to the C code for the “hello world” program below. BONUS: – a one page PDF guide with instructions on how to create and execute C programs, Python programs, and Shell scripts. What Can a C Program Do? C was initially used to develop operating systems, so it might not surprise you that the Linux kernel is written in C.
C can do pretty much anything you would want to do in computer programming. Some example applications include:. Operating systems.
Large programs. Databases. Desktop utilities.
Language compilers. Text/photo editors. Network drivers How to Write and Run a Program in C To demonstrate how to create a C program, compile it, and run it on the Raspberry Pi, we’ll make a simple program that will print “hello world” in the terminal.
The coding process in C consists of four steps:. Creating the source file. Compiling the program. Making the program executable. Executing the program Creating the Source File To start, open the Nano text editor and create a new file with a “.c” extension by entering this at the command prompt: sudo nano hello-world.c This file is where you’ll write the C code.
You can write the code in any text editor, just make sure to give the file a “.c” extension. Now, enter this code into Nano. After entering the code, enter Ctrl-X and Y to save and exit Nano. Compiling the Program Code written in C will need to be compiled before it can be run on a computer. Compiling is the process of converting the code you write into machine readable instructions that can be understood by the computer’s processor. When you compile your source file, a new compiled file gets created.
For example, entering the command below will compile hello-world.c into a new file called myfirstcprogram: gcc hello-world.c -o myfirstcprogram Making the Program Executable Now we need to make the compiled file executable. To do that, we just need to change the file permissions.
Enter this at the command prompt: chmod +x myfirstcprogram Executing the Program Now all we need to do to run the compiled, executable, C program is enter this at the command prompt:./myfirstcprogram Hope this helps you get a basic idea on how to get started programming in C on the Raspberry Pi. If you have any questions, please leave a comment below, and if you know anyone who could enjoy this information, please share it! You can also get our tutorials in your email by subscribing!
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