Programming Forums > Script Programming > Python

coldDeath · Aug 19th, 2005, 2:22 AM

Python - A Programmers Introduction

This is an introduction to Python. Instead of being for people new to
programming, it is for programmers who want to learn the language as
painlessly as possible.

Python is a Scripting Language. It's homepage is http://www.python.org
From there you can download the lastest release of Python.

Running Code
A great thing about Python is the Interpretor. You can type a bit of
code in and it executes it straight away. It is very useful for testing
quick bits of code.
You can use the interpretor, or you can make a file and save it as .py
you can run .py files using the Interpretor. Or on Linux, type the command

python filename.py

Comments
Comments in Python are shown by the hash symbol (#)

(Toggle Plain Text)

 #I am a comment i do not affect the code

Variables
When you declare a variables in Python, it takes an educated guess at
what type it is.

String

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my_string = "Hello World!"

Integer

(Toggle Plain Text)

my_int = 12

Float

(Toggle Plain Text)

my_float = 2.3

Long

(Toggle Plain Text)

my_long = 10L

Mulitple assignment
[code]var_1,var_2,var_3=1,2,3

Output
The most simple form of output is the print function.
It displays content to the screen.

It's syntax is: print content

Example:

(Toggle Plain Text)

print my_int #prints 12
print mystring, my_float #prints Hello World! 2.3
print "Hello" #prints hello
print 5 #prints 5
print "I like\nNewlines" # \n makes a new line

Lists

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my_list = ['hello',1,2,3,'coldDeath']

That makes a new list, lists can contain any variable types, even other lists.
Note that the start with 0.

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print my_list #prints ['hello',1,2,3,'coldDeath']
print my_list[4] #prints 'coldDeath'

Operations
You can perform many operations to variable.

Examples:

(Toggle Plain Text)

my_int * 10 #prints 120
my_float + 11.2 #prints 13.5
10 / 5 #prints 2
100 - 54 #prints 46
my_string + "!!!!!" #prints Hello World!!!!!!

If statements
Python uses whitespace, it makes code clearer and requires less typing.
For those coming from C++ or the like, Python doesn't have a switch statement
so you must use if statements, which is just as easy.

Example:

(Toggle Plain Text)

if my_int < 15: #True because my_int is 12
	print"my_int was less than 15"
elif my_int >= 16: #Else if statement
	print"my_int was greater than or equal to 16"
else: #Else statement
	print"my_int must be 15"

While loops
While loops are the easiest type of loop in Python.

Example:

(Toggle Plain Text)

count = 0 #integer
while count < 10:
	print count #print the variable
	count += 1	#Count = Count + 1

That would print out the numbers 1 - 10.

For loops
For loops in Python are different to most languages, the best way to see how they
work is to see an example!

Example:

(Toggle Plain Text)

for i in range(1,11): #range (1,11) means 1,2,3,4,5,6,7,8,9,10,11
	print i

Easy!

Functions
Functions in Python are easy, we use the keyword def to show we are defining
a function, then we have the function name then a bracket, the arguments
and another bracket.

(Toggle Plain Text)

def checkforprime(n):
	if (n < 2):
		return False
	for i in range(int(sqrt(n)) + 1)[2:]:
		if n % i == 0:
			return False
	return True

That takes a number as its argument and returns true if it is prime, and false if it isn't.
We call a function like this:

(Toggle Plain Text)

checkforprime(99)

Useful Stuff

(Toggle Plain Text)

range(1,10) #make a list from 1 to 10
pass #does nothing at all. Used when a statement requires no action
len(variable) #prints the length of the variable in the argument

Further Reading
If you want to go further with Python, you should read this tutorial:
http://docs.python.org/tut/tut.html
Remember that this tutorial doesn't cover much of the Python language,
but it should help you on your way.

Have fun!, sorry if i left anything out or made any mistakes.

Ooble · Aug 19th, 2005, 7:21 AM

Looks pretty good for someone coming from another programming language. You may wish to PM Big K and ask him to move this to the tutorials section.

Infinite Recursion · Aug 19th, 2005, 7:59 AM

Correct me if I am wrong... I haven't tinkered with Python as much as most of you.

If I wanted a block of code within my if statement to be executed... the indentations MUST be there. Correct? Would it be wrong to enclose the block in { }?

big_k105 · Aug 19th, 2005, 8:02 AM

Yeah the only way that you tell blocks is by the white space. Python actually just looks for the whitespace so it would by like this

(Toggle Plain Text)

if true:
     do this
     do this

Cerulean · Aug 19th, 2005, 8:18 AM

Quote:

If I wanted a block of code within my if statement to be executed... the indentations MUST be there. Correct? Would it be wrong to enclose the block in { }?

Yeah, precisely as Big K said. The colons are only part of the syntax because the creators of Python noticed that it really does add to readability, and gives writers of auto-indenters an easier time.
The amount of whitespace you use is up to you, the interpreter is smart enough to latch on to the fact you're using two spaces for your blocks, or a tab character, etc. The Python style guide, however, recommends you use four spaces (and also that you put spaces after each argument to a function, except the last argument :p)

Infinite Recursion · Aug 19th, 2005, 8:24 AM

Man, that kinda sucks... I like my { }. Personally, using the { } instead of a single : followed by indentation makes it more readable to me. I remember the days when I had to write code on grid paper to make sure the columns matched up correctly, because the language based its compile procedures depending on which column you were in, I forgot what language that was though... it was around the earlier 90s though.

skuinders · Aug 19th, 2005, 8:53 AM

I think Python is easy to read and write. HOWEVER, if you ever have to run code that has lost it's formatting, it is a pain in the ass to get back the correct indentation. At least with braces, the end of a block is obvious.

coldDeath · Aug 19th, 2005, 9:28 AM

I should have said about whitespace, but i didn't think twice about it.

Also i forgot the [/code] in the Multiple assignment bit, so the output part got stuck in the code tags.

big_k105 · Aug 19th, 2005, 9:31 AM

IR, RPG you have to have things in the right columns so the compiler knows what everything does.

http://www.99-bottles-of-beer.net/la...g-400-497.html

there might be another tho

Moldz · Aug 19th, 2005, 10:07 AM

The spaces versus {} trips up a lot of programmers when they first start using python. But it is amazing how quickly you adjust and then actually start to like it.

Aug 19th, 2005, 2:22 AM	#1
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 3	Python - A Programmers Introduction Python - A Programmers Introduction This is an introduction to Python. Instead of being for people new to programming, it is for programmers who want to learn the language as painlessly as possible. Python is a Scripting Language. It's homepage is http://www.python.org From there you can download the lastest release of Python. Running Code A great thing about Python is the Interpretor. You can type a bit of code in and it executes it straight away. It is very useful for testing quick bits of code. You can use the interpretor, or you can make a file and save it as .py you can run .py files using the Interpretor. Or on Linux, type the command python filename.py Comments Comments in Python are shown by the hash symbol (#) (Toggle Plain Text) #I am a comment i do not affect the code #I am a comment i do not affect the code Variables When you declare a variables in Python, it takes an educated guess at what type it is. String (Toggle Plain Text) my_string = "Hello World!" my_string = "Hello World!" Integer (Toggle Plain Text) my_int = 12 my_int = 12 Float (Toggle Plain Text) my_float = 2.3 my_float = 2.3 Long (Toggle Plain Text) my_long = 10L my_long = 10L Mulitple assignment [code]var_1,var_2,var_3=1,2,3 Output The most simple form of output is the print function. It displays content to the screen. It's syntax is: print content Example: (Toggle Plain Text) print my_int #prints 12 print mystring, my_float #prints Hello World! 2.3 print "Hello" #prints hello print 5 #prints 5 print "I like\nNewlines" # \n makes a new line print my_int #prints 12 print mystring, my_float #prints Hello World! 2.3 print "Hello" #prints hello print 5 #prints 5 print "I like\nNewlines" # \n makes a new line Lists (Toggle Plain Text) my_list = ['hello',1,2,3,'coldDeath'] my_list = ['hello',1,2,3,'coldDeath'] That makes a new list, lists can contain any variable types, even other lists. Note that the start with 0. (Toggle Plain Text) print my_list #prints ['hello',1,2,3,'coldDeath'] print my_list[4] #prints 'coldDeath' print my_list #prints ['hello',1,2,3,'coldDeath'] print my_list[4] #prints 'coldDeath' Operations You can perform many operations to variable. Examples: (Toggle Plain Text) my_int * 10 #prints 120 my_float + 11.2 #prints 13.5 10 / 5 #prints 2 100 - 54 #prints 46 my_string + "!!!!!" #prints Hello World!!!!!! my_int * 10 #prints 120 my_float + 11.2 #prints 13.5 10 / 5 #prints 2 100 - 54 #prints 46 my_string + "!!!!!" #prints Hello World!!!!!! If statements Python uses whitespace, it makes code clearer and requires less typing. For those coming from C++ or the like, Python doesn't have a switch statement so you must use if statements, which is just as easy. Example: (Toggle Plain Text) if my_int < 15: #True because my_int is 12 print"my_int was less than 15" elif my_int >= 16: #Else if statement print"my_int was greater than or equal to 16" else: #Else statement print"my_int must be 15" if my_int < 15: #True because my_int is 12 print"my_int was less than 15" elif my_int >= 16: #Else if statement print"my_int was greater than or equal to 16" else: #Else statement print"my_int must be 15" While loops While loops are the easiest type of loop in Python. Example: (Toggle Plain Text) count = 0 #integer while count < 10: print count #print the variable count += 1 #Count = Count + 1 count = 0 #integer while count < 10: print count #print the variable count += 1 #Count = Count + 1 That would print out the numbers 1 - 10. For loops For loops in Python are different to most languages, the best way to see how they work is to see an example! Example: (Toggle Plain Text) for i in range(1,11): #range (1,11) means 1,2,3,4,5,6,7,8,9,10,11 print i for i in range(1,11): #range (1,11) means 1,2,3,4,5,6,7,8,9,10,11 print i Easy! Functions Functions in Python are easy, we use the keyword def to show we are defining a function, then we have the function name then a bracket, the arguments and another bracket. (Toggle Plain Text) def checkforprime(n): if (n < 2): return False for i in range(int(sqrt(n)) + 1)[2:]: if n % i == 0: return False return True def checkforprime(n): if (n < 2): return False for i in range(int(sqrt(n)) + 1)[2:]: if n % i == 0: return False return True That takes a number as its argument and returns true if it is prime, and false if it isn't. We call a function like this: (Toggle Plain Text) checkforprime(99) checkforprime(99) Useful Stuff (Toggle Plain Text) range(1,10) #make a list from 1 to 10 pass #does nothing at all. Used when a statement requires no action len(variable) #prints the length of the variable in the argument range(1,10) #make a list from 1 to 10 pass #does nothing at all. Used when a statement requires no action len(variable) #prints the length of the variable in the argument Further Reading If you want to go further with Python, you should read this tutorial: http://docs.python.org/tut/tut.html Remember that this tutorial doesn't cover much of the Python language, but it should help you on your way. Have fun!, sorry if i left anything out or made any mistakes.

Aug 19th, 2005, 7:21 AM	#2
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	Looks pretty good for someone coming from another programming language. You may wish to PM Big K and ask him to move this to the tutorials section. __________________ Me :: You :: Them

Aug 19th, 2005, 7:59 AM	#3
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	Correct me if I am wrong... I haven't tinkered with Python as much as most of you. If I wanted a block of code within my if statement to be executed... the indentations MUST be there. Correct? Would it be wrong to enclose the block in { }? __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Aug 19th, 2005, 8:02 AM	#4
big_k105 PFO Founder Join Date: Mar 2004 Location: Fargo, ND Posts: 1,623 Rep Power: 10	Yeah the only way that you tell blocks is by the white space. Python actually just looks for the whitespace so it would by like this (Toggle Plain Text) if true: do this do this if true: do this do this __________________ BIG K aka Kyle Programming Forums Kyle K Online Please do not PM or email me programming questions. Post them in the forums instead.

Aug 19th, 2005, 8:24 AM	#6
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	Man, that kinda sucks... I like my { }. Personally, using the { } instead of a single : followed by indentation makes it more readable to me. I remember the days when I had to write code on grid paper to make sure the columns matched up correctly, because the language based its compile procedures depending on which column you were in, I forgot what language that was though... it was around the earlier 90s though. __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Aug 19th, 2005, 8:53 AM	#7
skuinders Hobbyist Programmer Join Date: Jun 2005 Location: MA, US Posts: 204 Rep Power: 4	I think Python is easy to read and write. HOWEVER, if you ever have to run code that has lost it's formatting, it is a pain in the ass to get back the correct indentation. At least with braces, the end of a block is obvious. __________________ "A stupid man's report of what a clever man says can never be accurate, because he unconciously translates what he hears into something he can understand." - B. Russell http://web.bryant.edu/~srk2

Aug 19th, 2005, 9:28 AM	#8
coldDeath Expert Programmer Join Date: Aug 2005 Location: UK Posts: 862 Rep Power: 3	I should have said about whitespace, but i didn't think twice about it. Also i forgot the [/code] in the Multiple assignment bit, so the output part got stuck in the code tags.

Aug 19th, 2005, 9:31 AM	#9
big_k105 PFO Founder Join Date: Mar 2004 Location: Fargo, ND Posts: 1,623 Rep Power: 10	IR, RPG you have to have things in the right columns so the compiler knows what everything does. http://www.99-bottles-of-beer.net/la...g-400-497.html there might be another tho __________________ BIG K aka Kyle Programming Forums Kyle K Online Please do not PM or email me programming questions. Post them in the forums instead.

Aug 19th, 2005, 10:07 AM	#10
Moldz Programmer Join Date: Feb 2005 Posts: 54 Rep Power: 4	The spaces versus {} trips up a lot of programmers when they first start using python. But it is amazing how quickly you adjust and then actually start to like it.

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