- Introduction
- What is Python?
- Where is it used?
- When can I use it?
- What else do I need to know before I start?
- Getting Started
- Choosing the right Python version
- Downloading and Installing Python
- Figuring out how it works
- Lets start programming!
- The Python Syntax
- Hello World!
- Math Functions and Variables
- One more step..
- If, elif, and else
- While loop
- For loop and Lists
- Function Definitions
- Modules
- Simple Programs
- What next?
- Deciding what to do
- Finding out how to do it
- Programming and beyond!
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What is Python?
Python is an interpreted, object-oriented,
high-level programming language. This means the Python requires an
interpreter to run. It cannot be compiled in the way C++ can. It must
have the interpreter.
Some may think this is a disadvantage, but I think otherwise. With
Python, you can debug at the source level, increasing productivity. You
can write and test your programs instantly, and find any possible errors
in seconds!
--------------------
Where is it used?
Python can be ran on almost any OS. While it is not native to Windows machines, it is native to most Linux distributions. The great thing with Python is its flexibility and usefulness in many environments.
--------------------
When can I use it?
Python is not limited to your local
machine. You can write Python programs/scripts to interact with other
computers, either on your Local Area Network (LAN) or across the
Internet. Python can be used to make interactive webpages and some of
the best programs. You may know some programs made in Python. A few
examples include:
As you can see, many popular programs are created using Python. You can make these programs too!
--------------------
What else do I need to know before I start?
Python can become addicting! It is easy to
learn and easy to code with. Before you continue with this tutorial,
please have an urge or push to really start your Python Programming
career!
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Choosing the right Python version
Many people will have many different
opinions on which Python version to choose. Personally, I use either
Python 2.6 or 2.7. The reason I use 2.6 is because it is supported, meaning that it has the most support and additional modules as of this time. In the future, Python may offer support for versions 3.x.
I also use Python 2.7 because it is what some people call future-proof. This means that 2.7 was written after 3.x, so it offers some compatibility between the two.
Currently, Python 2.x would be your best bet. Name companies, such as
Google, still use the 2.x versions of Python. So can you. Do NOT feel
pressured to need the latest versions, they are not always the best.
In this case, functions are handled differently and some things have a different syntax. It can get confusing for a new user.
--------------------
Downloading and Installing Python
To download Python, you will need to visit their website:
http://python.org/
And their download page:
http://python.org/download/
You should have decided in the last section which version to download.
If you are still questioning which version to choose, just get python
2.7
For Windows, here are two of the MSI installer links:
Python 2.7.1 Windows Installer
Python 2.7.1 Windows X86-64 Installer
Once you have downloaded the appropriate file (if you are not sure, use
the first download link) run the MSI file and leave all options at
default. It should install at "C:\Python27" with the numbers as your
Python version. If it did not install that, no worries, anywhere is
fine.
If you are using Linux, you may find it easier to get Python using the
following video. (Note** Many Linux Distributions already include
Python.)
Once you have Python installed on your machine, move on to the next section.
--------------------
Figuring out how it works
For the rest of this Tutorial and Guide, I
will be explaining Python from a Windows point of view. I will include
how to run Python files from Linux, but I will not delve into Linux Text
Editors and the like.
To make sure Python is working, press the Windows Start Button (bottom
left) and type in "python" (assuming you have Windows Vista/7, if not,
use 'Run' to run "python") and press enter. You should see a DOS type of
box appear on the screen with the insertion mark ("_") after three
arrows '>>>'.
If you can see this, Python is installed correctly! Good job, now let's move on to coding!
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The Python Syntax
Python's syntax is extremely easy to
learn. Unlike many programming languages, it does NOT require a
semi-colon (";") at the end of every line. That is a change for most
people.
Another thing is that Python uses 'white-space' instead of curly
brackets ("{}") to separate functions and classes. This keeps the source
neat and very easy to understand. Due to the simple syntax and
readability of code, it is easy to pick up another coders work from
nearly any point in their project. This gives Python loads of flexibilty
with collaborative projects.
Another good thing to remember with Python is that it IS case sensitive.
This means that "apple" is different that "Apple". This is important.
I also want to point out now, you can add a comment to a Python program using the pound ('#') symbol. Use it like so:
Code:
#This is a comment!
Comments are ignored by the interpreter and usually are only used to
include version information or to keep notes on the source code.
--------------------
Hello World!
It is time for what many of you have been
waiting for. Programming. Scripting. Whatever you would like to call it.
It is starting now, so get ready!
Okay, so as with many programming languages, I will start out with a
simple program, which is called 'Hello World'. What this program will do
is display the text "Hello World!" on the screen and await user input
to close.
Alright, so you will need to open up IDLE (for Windows users). This can
be done by typing 'IDLE' in the Windows Vista/7 search box in the Start
Menu. Once that opens, go to 'File' and click 'New Window'. This gives
us a blank page for us to write out our programs.
Alright! All set up, time for some code!
Here is the first bit of code we will use:
Code:
print "Hello World!"
Do NOT copy that straight into IDLE. Instead, type it out yourself, you will benefit more in the end.
What this code does is tell Python to Display
(print to screen) the following to the screen. Since we enclosed the
text ("Hello World!") in quotes, that means it is a string. A string
just means text, no numbers. Simple.
So that one lines of code displays "Hello World!" to the screen. The
only problem is that if you try running this, it will close instantly,
so let us add some code to stop it.
Code:
print "Hello World!"
raw_input("Press <enter> to close.")
Type that out into your text editor.
"raw_input()" is a simple way to grab data from the user. It is called input.
You may have noticed the quotes in the "raw_input()". Let me explain.
That function by itself without the quotes ("raw_input()") would work
100% to keep your program from instantly shutting down, but the quotes
with text gives the user instruction of what to do. This is important.
So now that you have those two lines of code, either go to 'File' >
'Save' ('Save As') or press 'CTRL' + 'S'. This comes up with the save
window. Due to simplicity, you can save the file at your desktop. By
default, it should have the option to either save as a "*.txt" file or a
"*.py" file. In our case, we want a "*.py" file.
So type in the file name bar: "example.py"
Then hit 'Save'.
When you press enter, the program will end.
Another way you can run the program is to just press 'F5' after you save
it (while the IDLE text editor is open). This will open it in Python's
native debugger. This is very useful when writing large projects, as it
can pinpoint exact errors in your coding.
In Linux, simply type the following into the terminal to run the file:
If you have successfully ran the file, congratulations! If not, go back
up and read again. Time to get into some interesting concepts.
--------------------
Math Functions and Variables
In any programming language, Mathematics
and Variables are of KEY importance. You cannot possibly write a leading
program without them. They are they key to programming, so without
further ado, lets explain how they work in Python.
Firstly, a variable can hold assorted types of data.
These include:
- Integers (int)
- Strings (str)
- Boolean Values (True or False)
We will cover those three in this section.
In Python, it is beyond easy to declare a variable. All you have to do
is type the variable name and its value. A variable can be named nearly
anything (do not use spaces though!) so it is very flexible. In my
examples, I will use an assortment of words and single letters as
variables.
This is how you declare a string variable:
Code:
x = "This is a string"
What happened? First, you have the variable name (in this case 'x').
Then, you put an '=' sign. Finally, you put its value, enclosed in
quotes. With python, you can use single quotes or double quotes, the
choice is up to you.
Now let us use the integer variable type.
Could that get any easier? Again, all you have to do is type the
variable name, an equal sign, and its value. With integers, you do not
use quotes. If you do use quotes with a number, it will be treated as a
string and NOT a number. So with integers, leave out the quotes.
Finally, we have the Boolean variable type. This holds only two
different options. True or False. You declare Boolean variables like
this:
Simple. You either write 'True' or 'False' (remember, case matters!).
Now that Variables are covered, it is time for basic math functions.
The first one I will cover it addition and subtraction.
If you can program, you should already know how this works, mathematically, but let me show you how it works in Python.
You can use IDLE for this. Use this snippet of code:
Code:
print 4+5
print 7-3
If you run that program, you will get the following output:
Basic math. With addition and subtraction, you can only use integer values.
Now, multiplication and division.
Multiplication ("*") can be handled with String variables and Integer variables. For example, use the following snippet of code:
Code:
x = 5
y = "5"
print x * 5
print y * 5
Your output will be:
For the integer variable, it is self-explanatory, basic math. However,
the string variable acted differently! When you multiply a string
variable, it just repeats itself. Simple enough, right?
Now time for division (and modulus).
To divide with Python, use the division sign ("/")
Your output will be '5'.
With Python, if you try dividing numbers that will result in a decimal
value, you have to include a decimal place in the operation. Let me show
you in action.
Code:
print 20 / 3
print 20 / 3.0
If you run that, you will get the following output:
The simple ".0" makes a big difference. Always remember to include a decimal place somewhere when using division!
Earlier, I mentioned modulus ('%') with division, because they are very
similar. When you were younger, you were probably taught how to divide
and then how to 'leave the remainder'. This is exactly what modulus
does. It does the division and gives you the remainder. Lets see how it
works.
Code:
print 20 % 5
print 20 % 3
Your output will be:
Simple. All modulus does if give you the remainder.
The last math function I will show you is exponents ('**'). An exponent
tells you how many times to multiply a number. For example, '6**3' is
the same as '6*6*6'. Let us see Python work this out.
Your output will be:
Simple. You should have already been familiar with all of these math operations, but now you know how to utilize it in Python!
One more thing with variables..
They can either be local, or global. This will be important later in the
tutorial, when function definitions are included, but this is how you
make a variable global (used everywhere in the program).
With 'x' being the variable.
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If, elif, and else
In Python, you will want to check against user input at some point, so the if statement will come in handy. Before I show you the code for it, let me tell you about it.
The 'if' statement pretty much just checks against something, and
returns a result based on the answer. Let me give you an example of
where you have to enter the correct phrase in order to see the
"Success!" text.
Code:
x = raw_input("Password: ")
if x == 'lemon':
print 'I love LEMONS!'
elif x == 'apple':
print 'I hate APPLES!'
else:
print 'I have no idea what that is!'
Let us dissect this line by line.
In the first line, we get input from the user with the statement, "Password:". The user input is assigned to variable 'x'.
Next, we open our 'if statement' with the first condition. If 'x' (what
the user typed) is equal ('==') to (exactly) 'lemons', then do the
following (':') and display ('print') the text.
Firstly, 'if' must be lowercase. Secondly, you must use double equal
signs ('==') when using 'if/elif'. Thirdly, if you are checking for a
string, make sure the what you are checking (in this case 'lemon') is
enclosed in quotes. Finish it off with a colon then go to the next line.
The next line MUST be indented (4 spaces) in an if statement.
The 'elif' works exactly the same, EXCEPT that it handles every other
"check/question" after the initial "if". You can have an infinite number
of "elif's".
Finally, 'else'. This is only raised if the "if" and none of the "elif's" were met. So a way of thinking of all this is..
"If the user types in lemon, tell them you love lemons. But if they type
apple, tell them you hate apples. If they do not type one of those two,
tell them you don't know what they are saying."
That is how you can think of it, in English.
I suggest that you use the techniques you have learned so far to create a
simple program, such as a calculator program (I will post the source
below of a simple calculator). Until then.. lets move on!
--------------------
While loop
The 'while loop' is the most basic of
Python loops. What a loop does, is perform a series of events as long as
something is in a certain condition. That condition can be anything.
For example, your condition can be that if 'x = 5' then to perform
something 5 times. It is simple.
I will show you an example of a basic while loop.
Code:
x = 5
while x > 0:
print x
x = x - 1
print 'We are out of the loop!'
With this, your output will be:
Code:
5
4
3
2
1
We are out of the loop!
Now let me explain each part.
First, we declare a variable, but you already should know about that.
Next, is the while loop. What this does is check to see if 'x' is greater than
0. As long as x is larger than 0, it will execute the content in the
loop. Also notice the colon (':') at the end of the 'while loop' line.
Next, I have the program display what 'x' is currently set to.
Finally, I use basic math functions to reassign "x's" value. What I do
is set its value equal to one less than its current value. Without this,
the loop would go on forever.
This is a basis loop. You can check for other conditions as well, such as
Code:
while x == 3:
while x < 10:
Those are some other examples. You can probably think of many more.
To get out of a loop early, use the following code:
This simply takes (breaks) you from the loop and continues with the program.
--------------------
For loop and Lists
In Python, lists are very important, as
are for loops. They are used in order to create complex programs and to
create ease with variables.
A list, in Python, is a variable that holds multiple values. They are
similar to arrays in other languages. It is declared the same as any
other variable, except that it needs to be enclosed with brackets ("[]")
and separated with commas (",").
Code:
x = ["Item One", "Item Two", "Item Three"]
print x
print x[0]
print x[1]
print x[2]
When you run that in IDLE, you will get:
Code:
['Item One', 'Item Two', 'Item Three']
Item One
Item Two
Item Three
Now, let me explain it.
In the first line, we declare that variable 'x' will hold the list. We
start the list with an opening bracket ('[') and start with our first
item (notice that since it is in quotes, it is a string). You then
separate each item with a comma. Simple.
Next, you print (display) the list contents. That is also simple. Now
the next line is new! We told Python to print (display) 'x[0]'. Let me
explain this. When you work with list items, you will use brackets
('[]') rather than parenthesis. You are probably wondering though, why
did I say '0' instead of '1'? Well, with Python, as with most
programming languages, lists start with '0'. So when I say 'print x[0]',
I am telling Python to give me the first list items.
This is just the basics of lists. Later in this guide, I will mention a link to where you can learn further with Python lists.
Now, the 'for loop'. The for loops syntax is different that the while loop. Let me show you an example.
Code:
for i in xrange(5):
print i
Your output:
Python 'for loops' iterate over a list. This means it goes through ever item in the list to perform the loop.
You initialize the 'for loop' with "for" and then a variable. In this
case, I chose 'i'. Next, you have to include the word "in" and then the
function. In this case, "xrange()". This means that it will perform the
loop 5 times.
When I print "i" on the next line, it is for each iteration of the loop (remember, Python starts counting at '0').
This is a simple explanation of Python 'for loops'. There are many more
things you can do with them, all of which can be found in the Python Documentation.
Time to move on to Function Definitions.
--------------------
Function Definitions
Functions in Python are very important.
They separate areas of the code to not only organize it, but to utilize
it to its fullest potential. The first thing you have to do is define
it, with its name, and then write the contents of the function on the
following line(s).
Code:
def Xero():
print 'Here is some content!'
print 'And some more...!'
for i in xrange(5):
print 'Hello!'
Xero()
And your output in IDLE:
Code:
Here is some content!
And some more...!
Hello!
Hello!
Hello!
Hello!
Hello!
Alright, now let me explain it. You start it off with defining it
('def') and then whatever name you want followed by parenthesis ('()')
and a colon (':'). Then you indent (4 spaces) and begin writing you code
for that function!
To call the function, simply type the function name with parameters
('()'). Once the function is done, it will return back to the point to
where it was called. This is just a simple example of Python functions.
As a beginner, you will not need to fill the parameters.
--------------------
Modules
Modules, simply stated, are Python
programs that you call to use. They are Python scripts already written
by another person in order for you to have an easier time doing certain
functions. I will provide an example of one function, and you can find
any other on Google.
To call a function, you need to import it. To do this, simply type 'import' and the Python file name.
'Time' is a basic Python module that comes with the Python package that
you downloaded earlier. Now, it is time for us to use this module.
Type in the following code, and run it.
Code:
import time
print 'This box will close in 5 seconds!'
time.sleep(5)
Alright, so the first thing it does is import the time module. Simple
enough, right? Then I added a 'print' function, and finally the
"time.sleep(5)". This will stop (sleep) the program for five seconds. Be
noted, using 'time.sleep' will freeze the entire program for five
seconds. You will not be allowed input. You may also wonder.. how will
you know everything in a given module? Well, you can always look up the
documentation for it. Another thing you can do is this:
Code:
import time
dir(time)
Replace 'time' with any module of your choosing. What this does is list everything that the module defines.
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Calculator
In this section, I will show you some
source codes of simple programs, using the techniques I taught you in
this tutorial. I highly suggest that you try making the programs before
looking at my source.
The first program will be a simple calculator to handle addition, subtraction, multiplication, and division.
Here is my source code:
Code:
global x
x = 1
def main():
global x
print "\n\n\n1.) Addition\n2.) Subtraction\n3.) Multiplication\n4.) Division\n5.) Free Hand\n6.) Exit"
choice = int(raw_input("Pick an option (1-6): "))
if choice == 1:
Addition()
elif choice == 2:
Subtraction()
elif choice == 3:
Multiplication()
elif choice == 4:
Division()
elif choice == 5:
Free()
elif choice == 6:
x = 0
else:
print 'Invalid Choice!'
def Addition():
x = int(raw_input("First number: "))
y = int(raw_input("Second number: "))
print 'Your result is: ' + str(x+y)
def Subtraction():
x = int(raw_input("First number: "))
y = int(raw_input("Second number: "))
print 'Your result is: ' + str(x-y)
def Multiplication():
x = int(raw_input("First number: "))
y = int(raw_input("Second number: "))
print 'Your result is: ' + str(x*y)
def Division():
x = int(raw_input("First number: "))
y = int(raw_input("Second number: "))
print 'Your result is: ' + str(x/y)
def Free():
x = raw_input("First number: ")
print eval(x)
while x == 1:
main()
Learn from that source code. If you do not know what something does,
look it up on Google. Reading another's source, and learning from it is a
great experience for a coder, in my opinion.
Now, I have an example of a Logbook type of program. What this does, is
retrieve input from the user and stores it in a text document in a
human-readable form. Again, please learn from this source code:
Code:
global x
x = 1
def main():
global x
choice = int(raw_input("1.) Log a Person\n2.) Exit\n\nChoice (1-2): "))
if choice == 1:
Log()
elif choice == 2:
x =0
else:
print 'Invalid Choice!'
def Log():
name = raw_input("Name: ")
age = raw_input("Age: ")
gender = raw_input("Gender: ")
eye = raw_input("Eye Color: ")
f = open("datafile.txt", "a")
f.write("\n\n"+"-"*25+"\nName: "+name+"\nAge: "+age+"\nGender: "+gender+"\nEye Color: "+eye)
f.close()
print 'Log Successful!\n\n'
while x == 1:
main()
These two example should give you ideas and teach you the basics of
Python. Utilize them to learn and expand your knowledge, and don't
hesitate to ask question!
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Deciding what to do
No doubt that once you finish this
tutorial, you will want to make a cool program. Every new coder wants to
make something really cool and advanced, but face it, knowledge is key!
Don't take me wrong, I want you to test your limits, but you should
also be reasonable while doing so. If this is your first introduction
into the foray into programming, then of course you will not have all
the knowledge necessary to make that game or that crypter you had
thoughts on. As with everything, programming takes patience, practice,
and time.
Here is my advice to you, find something locally (at your computer) that
could be easier done with a small program. Look at the logbook. If you
sell items online, you can make something like that to log your sales.
You could even take it a step farther so it can retrieve data as well as
store data. Your imagination is the only limitation, so let your mind
be free when programming.
Find something that needs to be done, and start doing it!
--------------------
Finding out how to do it
A big block for many coders is that they
simply do not know how to do something. This can easily be fixed by
reading the appropriate documentation on what you are trying to
accomplish. For example, read the Python documentation to learn about
loads of different modules and functions.
Use other resources. Go to Google and simply search for what you need to
do. Simple. Search for "python lists" and you will get TONS of results.
It is all there!
Tutorials, videos, and ebooks. There are loads of great ebooks and video
tutorials for those who want to further expand their knowledge.
Personally, I suggest TheNewBoston for his video tutorials, and for ebooks, I suggest A Byte of Python. Those two are some of the leading resources for new Python programmers. I know they helped me!
--------------------
Programming and beyond!
Programming can not only be a job, but a
great hobby. If you can enjoy programming, and have a great imagination,
then there are no limits to what you can do with a computer! Use your
knowledge and expand it with tutorials and your own imagination. There
are no limits. Use your imagination! :)
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