An Introduction to Python

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					An Introduction to Python
             Michael DiRamio
    District School Board of Niagara




  Imperial Oil Summer Institute
               2006
               Summary
•   IDLE: a Python IDE
•   Output
•   Arithmetic
•   Variables
•   Input
•   Looping
•   Selection
 Most Important Feature in a
 Language: Documentation


• The symbol to start documentation in
  Python is ‘#’
   Interpreted Programming
          Languages
• Some programs are compiled, meaning
  that the code you write is translated to
  something the computer understands.
• Others are interpreted, meaning that
  your code is read, as is, by another
  program that then does what the
  program specifies.
• Python is an interpreted language.
      IDLE: A Python IDE
• Free IDE
  download at
  www.python.org
• Has both
  interactions
  window and
  program files
                   Interactions Window
         IDLE: Interaction
• Allows you to try out an expression with
  immediate results.
• Output is the result of the expression
       Activity: Exploration
• Play with the interactions window, see
  what the results are.
• Exploration is a good way to learn, and
  this window provides an easy
  opportunity to explore.
    IDLE: Writing Programs
• Programs can be written in files,
  saved, and run.
• The results are produced in the
  interactions window.
                     Output
• The output keyword in Python is “print”. print
  will output anything, Strings, numbers, etc.
• Note the difference between simply putting
  “Hello” in the interactions window, and
  putting print “Hello”

                                  >>>
     print 4 + 6                  10
     print "Hello"                Hello
       program                       output
      Activity: First Program
• Write a program (not in the interactions
  window, in a separate file) that prints
  the phrase “Hello World” on the screen
• Run this program (Run -> Run Module)
  and see the output produced in the
  interactions window
           Concatenation
• String concatenation is the “+” symbol


           >>> 'Hello ' + 'World'
           'Hello World'
                          “ or ‘ ?
• Python allows you to use either single
  or double quotes for Strings.
• This prevents needing special
  characters if you want to use a quote in
  your string.
 >>> print 'This contains "double quotes"'
 This contains "double quotes"
 >>> print "And here are 'single quotes' inside"
 And here are 'single quotes' inside
                  Math
• The standard arithmetic operations: +, -,
  /, *, % (remainder)
• Note: if you divide two integers, the
  result will be an integer
• More math functions like ceiling and
  floor are in the math module (see
  intermediate Python)
         Activity: Division
• Explore the difference between
5/2
and
5.0 / 2
               Variables
• Python variables      >>> x = 6
  don’t carry type.     >>> print x + 3
                        9
  You can assign a      >>> x = "Hello"
                        >>> print x
  variable to be a      Hello
  string, then assign   >>> print x + " world"
                        Hello world
  it to an integer
  later
                          Input
  • The method raw_input(string) returns a
    string the user has typed in
  • The parameter to raw_input is the
    prompt given to the user.
x = raw_input("<TYPE SOMETHING>")
print "The user typed: " + x
      Program
                      >>>
                      <TYPE SOMETHING>This is my input
                      The user typed: This is my input
                                                Output
                         Input
 • The string input can be converted to
   other types using conversion methods
   like int(string) and float(string)
x = raw_input("<TYPE A NUMBER> ")
y = int(x)
print y * 2
   Program
                                    >>>
                                    <TYPE A NUMBER> 11
                                    22
                                               Output
   Activity: Input Conversion
• Write a program that reads in a
  temperature in Fahrenheit and converts
  it to Celsius
• C = (F - 32) * 5 / 9
             Indentation
• Python doesn’t use brackets to define
  blocks of code
• Indentation tells the program where a
  section ends
• If a program isn’t properly indented
                 Loops
                                       >>>
                                       0
• The loop            i=0
                                       1
                                       2
  continues           while i < 10 :
                                       3
                        print i
  iterating as long     i=i+1
                                       4
                                       5
  as the condition    print "done!"
                                       6
  following “while”      Program
                                       7
                                       8
  remains true                         9
                                       done!
                                        Output
     Activity: Importance of
           Indentation
• Create a program that uses a loop, like
  the previous example.
• Now remove the indentation and try
  running the program
            Comparisions
• “==“ is used for equality testing
• Inequality is “!=“
• Inequalities are straight forward: <=, >=,
  <, >
              >>> print 8 < 15
              True
              >>> print 9 != 7
              True
                  Interactions Window
      Selection Statements
• if/elif/else
• Must have one if clause
• Followed by 0 or more elif (else if)
  clauses
• Followed by 0 or 1 else clause
              Selection Statements:
                     Example
                                  • Notice what
x = raw_input("[input please]")
x = int(x)                        happens when
if x < 10 :                       you remove the
    print "Small"
elif x < 20 :                     indentation.
    print "Medium"
elif x < 30 :
    print "Big"
else :                            >>>
    print "HUGE!"                 [input please]21
print "Done"                      Big
                                  Done
    Program
                                         Output
        Activity: Selection
• Write a program that reads in a number
  and determines if that number is even
  or odd.
          Use in Computer
           Programming
• Free IDE
• The interactions window allows students to
  quickly test out ideas.
• Lack of brackets keeps code uncluttered.
• Students *must* indent their code properly or
  it won’t function properly.
• Lightweight syntax prevents students from
  becoming lost in the picky details of a
  language.

				
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posted:4/12/2013
language:English
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