Python Programming
High School (9–10)
High School (11–12)
Undergraduate
General
Python Essentials › Errors and ExceptionsChapter 2Errors and Modules
Catch errors with try and except so that programs do not crash, and borrow ready-made tools from modules.
Part of Python Programming · Essentials (chapter 2)
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When Things Go Wrong: try and except
Every program meets bad input and surprises: a word where a number is needed, a zero to divide by, a key that is missing. A program that crashes is a poor program, and a program that hides its errors is a worse one. In this course you learn to read an error message and name the common errors, catch them with try and except so that the program goes on, use else and finally, and build a loop that asks until the user gives a good answer. You learn to raise your own errors with a clear message, and to choose between checking first and catching afterwards. A safe data reader is the project at the end. The practice runs your code on good and bad input and tells you which cases fail.
Import a Toolbox: Modules
A module is a toolbox of code that you can use in your own program. Someone has already written, tested and improved a function for the square root, for rolling a die, for the median of a list and for the number of days between two dates. In this course you import the math, random, statistics and datetime modules, use their tools to solve small everyday problems, and learn the ways of importing. A lesson on finding and choosing tools shows how to look inside a module with dir and help, how to read an import error, and which mistakes make an import fail. A dice laboratory is the project at the end: you roll a die hundreds of times and see how fair it is. The practice runs your code and tells you which results are wrong.