Variables, expressions, and statements.

http://dpaste.com/1764212/

Lets look at three components of many programming languages.

Three primary tools we will be working with are:

Statements - small parts of a program that do not necessarily return a result. A program is formed by a sequence of one or more statements.
Names (a.k.a. variables) - pointers to data stored in memory.
Expressions - combination of names, symbols, functions, and/or operators that return another value.

These three aspects are fundamental to programming in general and will be explored throughout this course.

Examples:
In Python, statements can take many forms and work with many programming elements such as names and operators.

Names are labels that point to a specific item in the computer's memory. Assignment statements are statements where we assign a name to a value, or memory location. Below, a_name points to the memory location of a_value.

>>> a_name = 'a_value'

Names, technically called identifiers, must start with an underscore (the "_" character) or a letter. Names can contain any sequence of letters, numbers, and underscores. Names cannot contain spaces or other special characters. Names are case sensetive, so 'Sunshine' and 'SUNSHINE' are two different names.

There are 33 reserved words that may not be used as names. The following table outlines Python's reserved words.

Python Reserved Words
False	None	True	and	assert
break	class	continue	def	del
else	except	finally	for	from
global	import	in	is	lambda
nonlocal	not	pass	raise	return
try	while	with

Expressions typically return some result. The result can then be assigned a name.

In the following example, the expression on the right hand side will be evaluated and then assigned to the name to the left of the '=' assignment operator.

>>> total = 35.9 + 24.29
>>> total
60.19

Basic examples of expressions include arithmetic operations. Operators are included in expressions and consist of symbols such as:

Common Operators
+	-	/	*	**

Here are some operators in action:

>>> 2 + 3 # Addition
5
>>> 3 - 2 # Subtraction
1
>>> 5 * 5 # Multiplication
25
>>> 10 / 5 # Division
2
>>> 3 ** 3 # Exponent
27

Learning Resources

Python for Informatics -- Chapter 2 (Slides, Printable Slides, Streaming Video, Download Video, Lecture Audio)

Assignment

Review the documents in the learning resources section.
Be sure to complete the excercises as we are here to practice.
Copy your completed excercises and share them via a pastebin service such as dPaste.

If you have any questions or difficulties post them here and we will work together to make sure that everyone has a positive learning experience. Please also post ideas and insights into these concepts. We can learn a lot from each others' perspectives and experience :-)

Task Discussion

Asier Iturralde Sarasola said:
Here are my solutions:

Python 2.7:

2.2

2.3

2.4

2.5

Python 3.2:

2.2

2.3

2.4

2.5
on April 12, 2012, 1:33 p.m.
Nicolas Figueroa said:

Exercises

on March 14, 2012, 4:43 p.m.
thayne said:

http://dpaste.com/hold/713728/

on March 8, 2012, 3:06 p.m.
thayne said:

http://dpaste.com/hold/713728/

on March 8, 2012, 2:52 p.m.
E.Mosso said:

Apparently IDLE doesn't recognize the print command.. So if I type print 4 then enter, it says invalid syntax. Would you know how I can remedy this? Or what program besides IDLE to use?

on Feb. 28, 2012, 3:21 p.m.

Coffe Bean said:

You might consider using ipython. It's a realise nice "interface" to python unless you want to go down the IDE route, in which case I suggest something like netbeans or similar.

on Feb. 28, 2012, 3:37 p.m. in reply to E.Mosso

RobG717 said:

If you are using version 3.x of Python, then IDLE is doing exactly what it should, as "print 4" is invalid syntax. The new correct syntax for the print function is "print(4)".

Now if you're using version 2.x, then I have no idea why that would be happening.

on Feb. 29, 2012, 11:46 a.m. in reply to E.Mosso
blanco_fam said:

Here are my results

http://dpaste.com/704739/

on Feb. 18, 2012, 5:41 a.m.
dvdjaco said:

Here go mine!

http://pastebin.com/wu2GVZb3

on Feb. 13, 2012, 10:56 a.m.
pierg75 said:

Here is my exercise:

http://dpaste.com/hold/700470/

on Feb. 9, 2012, 3:01 p.m.
Judith Elaine Bush said:

See my chapter 2 exercises at http://www.evernote.com/shard/s6/sh/2ef7ab1c-6d88-4064-a39e-0d596c2be552/49ebaf1183fe6349244f8faabf824e3d

on Feb. 8, 2012, 7:53 a.m.
gnuisance said:

Here are my completed exercises.

on Jan. 23, 2012, 7:43 a.m.
Ken Doman said:

Here's my chapter 2 exercises.

Chapter 2 Exercises

on Jan. 17, 2012, 1:17 p.m.
Anonym said:

Here are my answers for 2.2-2.5.

on Jan. 12, 2012, 2:10 p.m.
ulf_st said:

Here are my solutions to Excercises 2.2 - 2.5

Cheers!

on Dec. 29, 2011, 2:10 p.m.
Landon said:
Variables, Expressions and Statements

Exercise 2.2

Exercise 2.3

Exercise 2.4

Exercise 2.4 Gone Too Far

Exercise 2.5
on Dec. 28, 2011, 4:51 p.m.
Sparker said:

Hi Everyone! Finished my first set of exercises!

Exercises 2.2-2.5

on Dec. 21, 2011, 8:57 p.m.

Brylie Oxley said:

Good submission. Well documented!

on Dec. 27, 2011, 3:50 a.m. in reply to Sparker
Anonym said:

Exercises 2.2 - 2.5

on Dec. 7, 2011, 2:14 p.m.
Shannon said:

I got my first exercises posted, only 4 months after starting the Python 101 group! Everyone please have a toast with pie and soda! My exercises on pastebin:

2.2

2.3 simple and unrounded

2.3 rounded (using quantize as advised in Python 3.2 docs for money rounding, quite over my head)

2.4

2.5

on Nov. 11, 2011, 12:21 p.m.
Anonym said:

When I run the file

#!/usr/bin/python3

print ('Hello World!')

name = input ('What is your name?\n')
print ('Hello ',name,'!')

I get the error message "syntax error near unexpected token `'Hello World!''" Could someone point out to me what I'm doing wrong? It was running before....

on Nov. 9, 2011, 7:41 p.m.

Anonym said:

I deleted /python3 and typed it again. Then it worked fine. Could someone explain why it (ie., re-typing) worked? Thanks.

on Nov. 9, 2011, 8:23 p.m. in reply to Anonym