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Foundations of Python Programming: Functions First

Section 5.1 Intro: What we can do with Conditionals

So far, our programs have been a series of statements which always execute sequentially. But sometimes programs must change the statements they execute depending on the situation. For example, a messaging app might only set a message’s title bold if it has not been read by the user. Or a video game needs to update the position of all the characters that are not asleep. This is done with something called a selection or a conditional statement.
The following program changes the message that is printed, based on user input:
The program above accepts a body temperature from the user and checks to see if it indicates a fever. Lines 4-7 contain conditional statements. If the temperature is greater than 37.8 the print statement on line 5 executes, otherwise the print statement on line 7 exectutes. Conditional statements like this create a branching effect in our program: the program no longer runs strictly sequentially.
This chapter will further detail how to use conditional statements.

Subsection 5.1.1 Learning Goals

  • To understand boolean expressions and logical operators
  • To understand conditional execution
  • To be able to write a boolean function
  • To know when to use binary, unary, chained and nested conditional statements

Subsection 5.1.2 Objectives

  • To properly evaluate a (compound) boolean expression
  • To use parenthesis to properly demonstrate operator precedence
  • To use conditional statements to properly branch code
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