ITEC 109 2014spring ibarland

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functions-used
Syntax and Functions cheat-sheet

Clickable Index:

• Syntax
  1. Expressions
     • Literals
     • using a variable
     • function-call
     • operators
  2. Statements
     • assignment statement
     • function-definition
     • return-statement
     • for-loop
     • while-loop
• Functions we've used.
  • numeric-functions
    • sqrt
    • pow
    • max
    • min
    • int
  • string-functions
    • str
    • len
    • substring
    • string
    • string
  • File-Picture-Pixel-functions
    • pickAFile
    • makePicture
    • show
    • repaint
    • explore
    • getPixelAt
    • getRed
    • setRed
    • setGreen
    • setBlue
  • Turtle-functions
    • makeWorld
    • makeTurtle
    • forward
    • turn

Syntax

• Expressions
  • Literal values:
    • ints: 3, -99, …
    • floats: -3.14, 1.2e9, …
    • characters: 'x', '#', …
    • strings: "hello", "x", "", …
    • booleans: True, False.
    • the-none-value: None.
    • objects (e.g. picture-objects, color-objects, etc.)
  • Using a variable:

    variable

    Example: n, or sumSoFar
  • function call:

    namefunction( expression, expression, … )

    In words: “To call a function: functionName-openParen-arguments.”

    Examples:

    • sqrt(25.0)
    • pow(3,4)
    • len( "hello" )
    • substring( "hello", 2, 4 )
    • sqrt( 21.0 + 4.0 )
    • sqrt( len("abcdefghijklmnopqrstuvwxy") )
    • show( makePicture( pickAFile() ) )

  • Infix operators:

    expressionnumeric + expressionnumeric

    (Example: 3+4, n+len("hello")

    expressionnumeric * expressionnumeric

    and so on for the other numeric operators, / and - and %. Also:

    expressionstring + expressionstring

    and

    expressionnumeric >= expressionnumeric

    expressionboolean or expressionboolean

    expressionboolean and expressionboolean

    not expressionboolean

• Statements:
  • assignment-statement:

    namevar = expression

    Examples:

    • n = 8
    • poem = "Candy is dandy \ But liquor is quicker"
    • quizPct = float(quizScore) / float(quizPossible) * 100.0
    • theChosenFile = pickAFile()
    We see that this rule requires the variable-name on the left-hand-side and not vice-versa; 8 = n is not valid!

    Note that assigning to a variable does not return a value; this means you can't use it as part of a bigger expression: sqrt( 21.0 + x = 4).

    I suggest pronouncing = as “gets”, since represents an action (put a value into a particular variable (box)), and is not really about equality.

  • function-definition:

    def namefunction( variable, … ): statement ⋮

    important: The indentation is important! The statements must be indented underneath the def; that's how python can tell which statements are inside the function, from whatever statements you want after the function-definition.

    We call the variable a “parameter”; it's just like other variables except that it gets initialized when somebody calls the function.

    Note:If you have a function without a return at the end, python adds a “return None” for you.

  • return-statement:

    return expression

    Return-statements can only occur inside a function-definition; they are usually the last statement in the function. (And a common beginner bug is to have a return-statement inside a loop that you want to repeat many times — the return-statement exits the function completely, so it can't occur repeatedly!)

    Note:If you leave off the expression, python fills in “None” for you.

  • if-else statements:

    if expressionboolean: statement ⋮ else: statement ⋮

  • for-loop statement:

    for variableindex in range(expressionnumeric): statement ⋮

    The for-loop manages your index for you, making it hold every value in the range: it initializes it to 0, then it increments each time through the loop, while the index-variable is still in the range.

    You often have a so-far variable which is initialized just before the loop, and is updated inside the loop (and, once the loop finishes, your so-far variable holds the value you were interested in).

  • while-loop statement

    while expressionboolean: statement ⋮

Function summaries

#### numeric functions

# sqrt : float → float
# Return the square root of a given number.
#
sqrt( 25.0 ) ⇒ 5.0
 
# pow : float, float → float
# Return one number raised to another.
#
pow( 2.0, 5.0 )  ⇒ 32.0

# max: float, float → float
# return the larger of two given numbers.
#
max( 7.0, 2.0 ) ⇒ 7.0

# min: float, float → float
# return the smaller of two given numbers.
#
max( 7.0, 2.0 ) ⇒ 2.0


# random.randrange : int → int
# Return a random natural number less than the given input.
#
random.randRange(5) ⇒ 3
random.randRange(5) ⇒ 0
random.randRange(5) ⇒ 4


# int : float1 → int
# Convert a float to an int:
#
int(  4.9 ) ⇒ 4
int( 15.0 ) ⇒ 15
int( -2.3 ) ⇒ -2


 
#### string functions

# str : float2 → string
# Convert a given number to a string
#
str(15) ⇒ "15"


# len : string → int
# Return the number of characters in a given string.
#
len("hello") ⇒ 5

# substring : string, int, int → string
# Given some text, a start-index, and a stop-index,
# return the characters of `txt` from `start` up until (but not including) `stop`.
# Indices are 0-based.
#
substring( "radford", 3, 6) ⇒ "for"
substring( "radford", 0, 3) ⇒ "rad"


# string.upper : string → string
# Return an upper-case version of a given string.
#
string.upper( "hello" ) ⇒ "HELLO"

# string.capitalize : string → string
# Return a capitalized version of a given string.
#
string.upper( "hello" ) ⇒ "Hello"



#### File, Picture, Pixel functions

# pickAFile : None → string
# Return a filename as selected by the meatbag sitting at the keyboard.
#
pickAFile() ⇒ "C:/Users/CarnieTote/Documents/important file.docx"
pickAFile() ⇒ "C:/Users/CarnieTote/Documents/itec109/ufo.png"

# makePicture : string -> Picture
# Return a picture-object created from the provided filename.
#
makePicture( "ufo.png" ) ⇒ A picture with width 192 and height 47.

# show : Picture → None
# Display a Picture-object in a window on the screen.
#
show( makePicture("ufo.png") ) ⇒ None

# repaint : Picture → None
# Update the window where the indicated Picture-object has been previously displayed.
# Useful if any pixels have been modified since.
#
repaint( makePicture("ufo.png") ) ⇒ None

# explore : Picture → None
# Pull up a pixel-explorer tool for the indicated Picture-object.
#
explore( makePicture("ufo.png") ) ⇒ None

# getPixelAt : Picture, int, int → Pixel
# Return the individual pixel object at the specified (x,y) coordinates of the given Picture-object.
#
getPixelAt(makePicture("ufo.png"), 5, 5) ⇒ a Pixel with color=(255,255,0)

# getRed   : Pixel → int
# getGreen : Pixel → int
# getBlue  : Pixel → int
# Return a value in [0,256) — the redness/greenness/blueness of the given pixel.
#
getGreen( getPixelAt(makePicture("ufo.png"), 5, 5) ) ⇒ 255

# setRed   : Pixel, int → None
# setGreen : Pixel, int → None
# setBlue  : Pixel, int → None
# Change a pixel's red/green/blue to be the given number.
#
setBlue( getPixelAt(makePicture("ufo.png"), 5, 5), 22 ) ⇒ None



#### Turtle Functions

# makeWorld : int, int → World
# Return a World-object (a turtle-sandbox) of the given width & height.
#
makeWorld(20,30) ⇒ a 20-by-30 world with no turtles in it

# makeTurtle : World → Turtle
# Return a new turtle located at the center of the given world, facing north.
#
makeTurtle(makeWorld(20,30)) ⇒ a turtle at 0,0 facing 0.0

# forward : Turtle, float → None
# Move the indicated turtle forward the indicated number of pixels.

# turn : Turtle, float → None
# Rotate the indicated turtle the indicated number of degrees clockwise.
#
turn( makeTurtle(makeWorld(20,30)), 90 )
     

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©2014, Ian Barland, Radford University Last modified 2014.May.05 (Mon)

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