LPTHW Exercises 0-10

(1/13/2014 -- 6:30pm EST)

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ExerCise 0: The Setup

Why do exercises start at number 0?

What does "python" do when written in the terminal?

"CRTL + C" to stop your Python programs

explain cd, ls, mkdir (Bash basics)

Exercise 1

Python files (aka modules) should end with ".py" extension

Typing "python" into the command line starts the interpreter Typing "python my_file.py" executes that file

Create a file with the code below and run it

 print 'hello world'  print boy #### Try to understand what the error messages here mean

Exercise 2: Comments & printing

# character begins a comment
#### multiple pounds are acceptable for a comment

Why does the # in print "Hi # there." not get ignored?

The # in that code is inside a string, so it will be put into the string until the ending " character is hit. These pound characters are just considered characters and aren't considered comments.

How do I comment out multiple lines?

Put a # in front of each one.

Exercise 3: Numbers and math

Order of operations as you would expect with math

  5 + 10 * 2 --> 25  5 > 10 - 9  -->
  #### You should try, though, to always be explicit (generally true in coding)   5 + (10 * 2) --> 25

What is going on here with division?

 4 / 3 -->  14.0 / 3 --> 1.3333333333333333

What is modulus?

 4 % 3 --> 1

Exercise 4: Variables

   student_count = 20   auditor_count = 5   total_count = student_count + auditor_count

The words above ending in "_count" are variables

A variable is a name that references (or labels) a value

The program uses variables to keep track of values

The number 20 is a value (we can add it, subtract it, etc)

Here is stored in the variable called "student_count"

 print new_variable     # What happens if we run this? print "new_variable"   # how about this?

Extra Content: Statements & Expressions

An expression is a piece of code that reduces to a value

 5 + 7  # this expression reduces to (or represents) the number 12 2  # reduces to the value 2 'Learn' + 'Code'  # reduces to the value 'LearnCode'

A statement does not reduce to a value

 a = 5  # assignment of a value to a variable is a statement
     print (5 + 7)  #printing is a statement (addition here is also an expression)

Exercise 5: Intro to Strings

A string is a sequence of characters surrounded by quotes

 "boy" --> string 'boy' --> string  boy -->  variable name (you need to assign a value to it somewhere)   "2" --> string  2 --> number

Strings can be "interpolated" (aka variables inserted)

 print "Boy named %s" % "John" -->  "Boy named John" print "Boy is %d years old" % 2 -->  "Boy is 2 years old"

Exercises 7-10: Printing

To extend strings over multiple lines, use triple quotes

 example = """        This is a sample string        spread over multiple lines        """

To include quotes inside strings

"Alternating between single and double quotes will 'work' just fine"'It "works" in both directions'
"Alternatively, you can use \"backslashes\" instead"

The newline (\n) is a special character that adds a new line