Lab 4 Predicates and Conditionals

Solutions

Worksheet solns

Goals

• Review conditionals
• Practice writing predicates
• “Divide, Conquer, and Glue” (DCG): functions with conditionals

Lab Setup

• Find your partner
• Use CyberDuck to SFTP into your account on the cs.wellesley.edu server
• On the server, navigate to the cs111/download folder
• Download the lab04 folder to your Desktop (drag and drop it from the CyberDuck window)

• Open Thonny and view the relevant lab04 files

• Here is the worksheet as a google doc
• Open the document, then File -> Make a Copy.
• Then you can edit your copy with your answers.

Table of Contents

• Lab 4 Home
• Part 0: Warm up worksheet
• Part 1: Predicates and Functions
• Part 2: Conditionals
• Part 3: Buzzfeed-style quiz
• Reference: Using Conditionals to Disable testing code
• Knowledge Check

Big Questions

• What is a predicate, and how can you build a complex predicate out of multiple simpler predicates?
  Show Answer

  A predicate is a function that always returns a boolean value. To build a complex predicate from simple ones, the complex predicate function should call the simple functions and combine their result values using boolean operators into a single boolean that it can return.
• What is the difference between writing a series of if statements and a single if statement with multiple elif parts?
  Show Answer

  A series of if statements operate independently, and it's possible for more than one to trigger. A chain of if/elif statements guarantees that only the first statement whose condition is true will trigger, and others will be skipped even if their conditions are also true.