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Python: Creating a menu-driven program

Python: Creating a menu-driven program. Review. JES command area – program area Defining/using functions specifying a sequence of steps for what the function should do. JES Functions for file manipulation JES->Files JES Functions for interacting with user JES-->Input/Output

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Python: Creating a menu-driven program

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  1. Python: Creating a menu-driven program

  2. Review • JES command area – program area • Defining/using functions specifying a sequence of steps for what the function should do. • JES Functions for file manipulation JES->Files • JES Functions for interacting with user JES-->Input/Output • JES Functions for picture manipulation JES-->Pictures

  3. Reminder: Manipulating Pictures >>> pic1 = makeEmptyPicture(200,100) >>> seafoam = makeColor(153, 255, 204) >>> setAllPixelsToAColor(pic1, seafoam) >>> show(pic1) >>> addText(pic1,30,50,“hello") >>> pic2 = makePicture(pickAFile()) >>> show(pic2) • similarly can add rectangles, lines, etc.

  4. red=108 green=86 blue=142 y = 9 Color:(108,86,142) Position: (12,9) >>> pixel=getPixel(picture,12,9) >>> print pixel Pixel, red=108 green=86 blue=142 >>> value = getRed(pixel) >>> setRed (pixel, value+50) >>> setGreen(pixel, 0) >>> setBlue(pixel, getBlue(pixel)/2) x = 12

  5. red=108 red=158 green=86 Green=0 blue=142 Blue=121 y = 9 y = 9 Color:(108,86,142) Position: (12,9) Color:(158,0,121) Position: (12,9) >>> pixel=getPixel(picture,12,9) >>> print pixel Pixel, red=108 green=86 blue=142 >>> value = getRed(pixel) >>> setRed (pixel, value+50) >>> setGreen(pixel, 0) >>> setBlue(pixel, getBlue(pixel)/2) x = 12

  6. red=108 green=86 blue=142 y = 9 Color:(108,86,142) Position: (12,9) >>> pixel=getPixel(picture,12,9) >>> print pixel Pixel, red=108 green=86 blue=142 >>> redValue = getRed(pixel) >>> greenValue = getGreen(pixel) >>> blueValue = getBlue(pixel) >>> newColor = makeColor(redValue+50, 0, getBlue(pixel)/2) >>> setColor(pixel, newColor) x = 12

  7. red=158 Green=0 Blue=121 y = 9 Color:(158,0,121) Position: (12,9) >>> pixel=getPixel(picture,12,9) >>> print pixel Pixel, red=108 green=86 blue=142 >>> redValue = getRed(pixel) >>> greenValue = getGreen(pixel) >>> blueValue = getBlue(pixel) >>> newColor = makeColor(redValue+50, 0, getBlue(pixel)/2) >>> setColor(pixel, newColor) x = 12

  8. Repeating an action for all the pixels in a picture Example: for p ingetPixels(picture):    value = getRed(p)setRed(p, value*0.5)

  9. Repeating an action for all the pixels in a picturedecreaseRed() Example: def decreaseRed(picture): for p ingetPixels(picture):    value = getRed(p)setRed(p, value*0.5)

  10. More examples: • decreaseGreen() • decreaseBlue() • clearBlue() • lighten() • darken() • negative() • grayScale()

  11. Lab 9 Assignment – picture manipulation functions • Decrease red by 10% • Decrease green by 10% • Decrease blue by 10% • Make the picture darker by decreasing red, green, and blue by 10% • Make a grayscale version of the image and then negate it (B/W negative)

  12. Lab 10: Menu driven program – create your very own baby photoshop! Create a menu-driven picture manipulation function that allows the user to make various changes to images. Here is the algorithm: • welcome the user to your program • get the user to select a picture to work on • show(picture) • ask the user to select an option from a list of numbers: • reduce red • reduce green • reduce blue • posterize • grayscale • <a feature of your choice> • repaint(picture) • ask user whether to save the new picture, and if the response is “yes”, save it • show goodbye/thank you message

  13. Conditionals if age < 18: showInformation(“Sorry, not allowed to vote yet.”) else: showInformation(“Please select candidate.”)

  14. Relational Operators • a > b • a < b • a == b (equality) • a <= b (“less than or equal”) • a >= b (“greater than or equal”) • != (inequality) Note: The order of signs matters: =! =< => do not work! There should be no spaces inside the relational operator, so “a < = b” also does not work (See also Appendix A.4, p362)

  15. Escape characters Special characters that cannot be used directly as part of a string, eg: • \n – new line • \t – tab • \\ – backslash (\) • \’ – single quote Example: showInformation(“see you\nlater”)

  16. Saving to a file • setMediaPath():Prompts the user to pick a folder on the computer. JES then will look for files in that directory unless given a full path, i.e. one that starts with "c:\" • writePictureTo(picture, path):picture: the picture you want to be written out to a filepath: the path to the file you want the picture written toTakes a picture and a file name (string) as input, then writes the picture to the file as a JPEG. • Example: writePictureTo(pic, “mypic.jpg”)

  17. Steganography • From the Greek words stegein and graphein meaning “covered writing.” • Art and Science of hiding information in ways that prevent detection. • Can be used on audio, text, packet headers, or images • Similar to Cryptography • Cryptography: scrambles message • Steganography: hides message

  18. SteganographyEarly Examples In his history of the Persian Wars, Herodotus tells of a messenger who shaved his head and allowed a secret message to be tattooed on his scalp. He waited until his hair grew back. Then he journeyed to where the recipient awaited him and shaved his head again. The message was revealed. It was history’s first use of steganography.

  19. Ways to Hide the Image • Least Significant Bit (LSB) • One of most common techniques • Alters LSB of each pixel (3 bits out of 24) • Works best on Bitmaps in the color data and GIFs in the palette data. To hide letter C (1000011) in a file: Original: 01001101 01001110 01001110 01001111 01010000 01010000 01001111 Encoded: 01001101 01001110 01001110 01001110 01010000 01010001 01001111

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