1 / 22

Understanding Python Modules and Loops: A Guide to Effective Coding in CS111

This guide covers key concepts from CS111, focusing on using Python modules and for loops to build efficient programs. It explains how to import modules, such as the math module, and emphasizes the advantages of using built-in functions. The text provides practical examples of looping structures, detailing how to repeat tasks effectively through the use of the for loop. Additionally, it explores design patterns and initialization, showing how these concepts help in creating structured and efficient code. Ideal for beginners seeking to sharpen their Python skills.

perry
Télécharger la présentation

Understanding Python Modules and Loops: A Guide to Effective Coding in CS111

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Objectives • Review: Precedence/Arithmetic, importing modules • Definite for loops Sprenkle - CS111

  2. Exponentiation • Goal: compute -32 • Suggested: pow(-3, 2) • pow is a built-in function • How else could we get that? • For fun, what is 2 ** -3 ** 2 Sprenkle - CS111

  3. Python Libraries • Python has a rich library of functions and definitions available for your use • The library is broken into modules • A module is a file containing Python definitions and statements • Benefits of functions/definitions in modules • Don’t need to rewrite someone else’s code • If it’s in a module, it is a very efficient (in terms of computation speed and memory usage) Sprenkle - CS111

  4. Importing Modules • To use the definitions in a module, you must first import the module • Example: to use the math module’s definitions, use the the import statement: • Typically import statements are at top of program • To use, prepend constant or function with “modulename.” • Examples for constants: • math.e • Examples for functions: • math.sqrt import math module_example.py Sprenkle - CS111

  5. Using Modules • Alternatively can import only a subset of the module: • Syntax: from <library> import <name1>, <name2>, … • Example: from math import pi • Then, can use just pi instead of math.pi in program Sprenkle - CS111

  6. Finding Modules To Use • How do I know if some code that I want already exists? • Python Library Reference: • http://docs.python.org/lib/lib.html • For example, string module has functions/constants for manipulating strings • For the most part, to practice, in the beginning you will write most of your code from scratch Sprenkle - CS111

  7. Programming Building Blocks • Each type of statement is a building block • Initialization/Assignment • Arithmetic, string concatenation, input/raw_input • Print • Import • We can combine them to create more complex programs • Solutions to problems import Assign. print import Assign. print Assign. Assign. print Sprenkle - CS111

  8. Design Patterns • General, repeatable solution to a commonly occurring problem in software design • Template for solution Sprenkle - CS111

  9. Design Patterns • General, repeatable solution to a commonly occurring problem in software design • Template for solution • Example (Standard Algorithm) • Get input from user • Do some computation • Display output • Today: learn new building block, new design pattern Assign. x = input(“…”) ans = … print ans Assign. print Sprenkle - CS111

  10. Looping/Repetition Make PB&J sandwich Repeat 10 times Make 10 PB&J sandwiches Make PB&J sandwich Sprenkle - CS111

  11. The for Loop • Good for when know how many times loop will execute • Repeat N times Loop variable Keywords Loop header for x in xrange(10): Make 10 PB&J sandwiches Make PB&J sandwich Loop body Sprenkle - CS111

  12. Using theFor Loop • Good for when know how many times loop will execute • Repeat N times for x in xrange(10): statement_1 statement_2 … statement_n Times to repeat • - “Body” of for loop • Gets repeated • Note indentation Sprenkle - CS111

  13. Using theFor Loop • If only one statement to repeat for x in xrange(5): print “Hello!” simple_for.py Sprenkle - CS111

  14. What Goes in the Loop Body? • Make PB&J Sandwich • Gather materials (bread, PB, J, knives, plate) • Open bread • Put 2 pieces of bread on plate • Spread PB on one side of one slice • Spread Jelly on one side of one slice • Place PB-side facedown on Jelly-side of bread • Close bread • Clean knife • Put away materials for x in xrange(10): Make PB&J sandwich Sprenkle - CS111

  15. What Goes in the Loop Body? • Make PB&J Sandwich • Gather materials (bread, PB, J, knives, plate) • Open bread • Put 2 pieces of bread on plate • Spread PB on one side of one slice • Spread Jelly on one side of one slice • Place PB-side facedown on Jelly-side of bread • Close bread • Clean knife • Put away materials Initialization Loop Body Finalization Sprenkle - CS111

  16. Using theFor Loop • Good for when know how many times loop will execute • Repeat N times for x in xrange(10): statement_1 statement_2 … statement_n Times to repeat • - “Body” of for loop • Gets repeated • Note indentation Sprenkle - CS111

  17. Analyzing xrange() • xrange is a built-in function • What does xrange do, exactly? xrange_analysis.py Sprenkle - CS111

  18. xrange([start,] stop[, step]) • What does the above signature mean? Sprenkle - CS111

  19. xrange([start,] stop[, step]) • 1 argument: xrange(stop) • 2 arguments: xrange(start, stop) • 3 arguments: xrange(start, stop, step) using_xrange.py Sprenkle - CS111

  20. xrange([start,] stop[, step]) • 1 argument: xrange(stop) • Iterates from 0 to stop-1 with step=1 • 2 arguments: xrange(start, stop) • Iterates from start to stop-1 with step=1 • 3 arguments: xrange(start, stop, step) • Iterates from start to stop-1 with step size=step • Note that with negative numbers, using_xrange.py Sprenkle - CS111

  21. Practice • Add 5 numbers, inputted by the user • Average 5 numbers inputted by the user Sprenkle - CS111

  22. Accumulator Design Pattern • Initialize accumulator variable • Loop until done • Update the value of the accumulator • Display result Sprenkle - CS111

More Related