Python Input and Output

• This presentation introduces the concepts of input and output in Python programming using abstractions.
• The slides are ported to Python by James Pope, and were last updated on 2023/10/20.

Introduction to Input and Output

• Discussed are standard input/output, standard drawing, fractal drawings, animation, and standard audio.

Basic Programming Building Blocks

• Programs consist of objects, functions, modules, and graphics/sound/image components.
• I/O (input/output) facilitates interaction with the outside world.
• The basic elements include primitive data types, text I/O, and assignment statements.

Input and Output Goal

• Python programs should be able to interact with the external environment through devices for input and output.
• Input devices include keyboards, trackpads, cameras, and microphones.
• Output devices include displays, speakers and printers.
• Input and output are defined through abstractions, using OS(Operating System) functionality to connect Python programs with actual devices.

Abstraction Explanation

• Abstraction plays a key role in grasping computation
• An abstraction exists as an idea; for example, printing represents the concept of a program generating text as output.
• Effective abstractions simplify and unify understanding for real-world artifacts.

Terminal Abstraction

• A terminal provides input to and receives output from programs.
• The command line is one example of standard input.
• Standard output gets sent to stream.

Input-Output Abstraction

• A program receives command-line arguments as one form of input.
• A Python program processes input and generates output to a standard output stream.

Command-Line Input Review

• Command-line input, as an abstraction, provides arguments (strings) to a program.
• At runtime the strings are available as argv[0], argv[1], etc.
• It's necessary to call system conversion methods to convert the strings to other data types.

Standard Output

• Standard output stream is an abstraction that has no limit.
• The end of the standard output stream has strings added through stdio.writeln().
• The standard output stream is sent to the terminal application by default.

Improved Input-Output Abstraction

• Standard input stream is added to the model to allow infinite input.
• Python programs can now receive arguments from the command line, take input via the standard input stream, and produce output via the standard output stream.

Standard Input Abstraction

• Standard input stream represents an infinite input sequence that has no limit.
• Standard input offers advantages over command-line input.
  • New arguments can be provided while a program runs.
  • There is no limit to the amount of data that the input can have.
  • Conversion to primitive types is explicitly handled through dedicated methods.

StdIO Library Details

• The stdio library was created for educational purposes but has broad utility.
• The library implements abstractions that were developed for UNIX systems in the 1970's.
• It is downloadable for free from the associated booksite
• Functions include:
  • isEmpty(): Determines if there are no more values, will return a boolean value
  • readInt(): Reads an integer value as input
  • readFloat(): Reads a value of double type
  • readBool(): Reads a boolean value .
  • readString(): Reads a String type value
  • readAllStrings(): Reads the rest of the text
• Includes other functions like:
  • write(s): Puts s on the output stream
  • writeln(): Puts a newline on the output stream
  • writeln(String s): Puts s, then a newline on the stream
  • writef(String f,...): Formatted output

Std-IO Library Reason

• The print () function could be used, but this library creates:
  • A consistent and simpleI/O abstractions set
  • Enables to make output that is system, language, and locale independent

Usage of writef

• It provides formatted output using conversion specifications within a format string.
• stdio.writef('%7.5f', math.pi) is an example of its usage.
• The parts are the format string, the conversion specification which number to print , the field width and the conversion code
• The type and code, as well as sample format strings, converted string values for output, can be:
  • int d, '%14d', '512'
  • float e, '%14.4e', '1.5952e+03' -String s, '%-14.5s', 'Hello'

Interactive Input and Output

• Mixes input and output streams.
• Prompts user to enter input on standard input stream.

Input Application: Average the Numbers

• Reads a stream of numbers and compute their average.
• The end of the stream is specified by (standard for decades) or (Windows). -There is no limit on input size or the input an output, which can be interleaved through console

Applications of Standard I/O

• Both streams are infinite
• Data and results can be kept in files or using piping for connecting programs.

Data Redirection

• Standard output is commonly redirected to files.
• Input to a program can be redirected from a file to standard input.

Piping Data

• Keeps data in files on systems
• Piping connects the standard output of one program to the standard input of another.
• There are no data limits

Streaming Algorithms Context

• Streaming algorithms have evolved due to limitations in available memory
• Redirection and piping allowed the programs to handle more data than the computers could actually handle.

Modern Streaming Algorithms

• Streaming algorithms are essential now
• They enable the programs to handle much higher amount of data than the computers' capacity

Stddraw Library Purpose

• Stddraw library enables creating a drawing.
• The library provides standard output streams
• It is mainly used for educational purposes
• It is available for download from the course booksite Includes useful functions:
• line(x0, y0, x1, y1)
• point(x, y)
• text(x, y, s)
• circle(x, y, r)
• square(x, y, r)
• polygon(x, y, r) places.gif,.jpg or .png file .
• setPenRadius(r)
• setPenColor(c)
• setXscale(x0, x1)
• setYscale(y0, y1)
• show(dt)

Plot examples with Stddraw Library

• Examples of functions:
  • line() draws a line from point (x0, y0) to (x1, y1)
  • point() plots a point at coordinates (x, y)
  • polygon() draws a polygon using specified x and y coordinates

'Hello, World' Example

• Program to draw something in Java
• The program draws a triangle, set the pen Radius and set a text string

Data Visualization

• Stdraw is commonly used for this feature
• Uses functions like setXscale, setYscale, and point to plot points.

Drawing Functions

• Code that plots the function that takes N samples regularly spaced, with setXscale to X and setYscale to y, then implements the logic
• The x[i] = math.pi * i / N is mainly how the line and spacing are calculated
• The y[i] = math.sin(4x[i]) + math.sin(20x[i]) relates to the function

Random Games in StdDrawContext

• A random game, where:
  • A triangle is drawn that has the labels R, G, and B for the vertices
  • Each has a probability
  • Each has a certain logic for calculating values such as new x and new y

Color Customization

• Color point can be customized according to random vertex chosen using
• Color points can be modified using stddraw.setPenColor()

IFS

• Iterated Function Systems systems use iterative computations for generation
• They use formulas in computation for generating data
• The coefficients come from standard input

Animation Explanation

• Animation is created through StdDraw library toolset
• Screen is cleared, next object is moved, and the next object is drawn
• Illusion of motion is created, and the display will pause
• The ball is bounced, the position is set and constantly updated

Standard Audio

• Sound is a reaction to the vibrations of molecules
• A musical tone is a steady sound with a periodic vibration
• A pure tone is described via some sinusoidal waveform
• Western musical scale has 12 notes

Frequency in Hz

• Concert A is 440 Hz normally

Digital Audio Function Explanation

• The arrays will save sampled waves, that are same as when plotting to a function
• There are samples/sec that have examples such as 5 512, 11 025 and 22 050
• There is also CD standard, which equals 44100
• All sounds manipulated can be created on a new float function

Stdaudio library Usage

• Plays sound wave
• Converts to and from standard .wav files
• Usual public class stdaudio operations include
  • playFile(file)
  • playSamples(float[] a),
  • playSample(s) -save(file, a) -read(file)

Music Creation Example

• Generates sound signals through math.sin function for different frequencies
• Can generate a sin function that can play tones