Python - Zelle book uses eval(), is it wrong?

Question

PLEASE NOTE: This is NOT about the use of eval(), it is about the potential quality (or lack thereof) of a book it is used and taught in. SO already has countless threads ab

Answer 1

Yes, it's wrong. But I think I know why it's in there.

Lots of people use input() in Python 2.x, which is a very unfortunately named function since it doesn't just read input, it also evaluates it. The converter 2to3 converts each use of input() to eval(input()), as you can see:

$ cat test.py
x = input("Enter your number: ")

$ 2to3 test.py
RefactoringTool: Skipping implicit fixer: buffer
RefactoringTool: Skipping implicit fixer: idioms
RefactoringTool: Skipping implicit fixer: set_literal
RefactoringTool: Skipping implicit fixer: ws_comma
RefactoringTool: Refactored test.py
--- test.py     (original)
+++ test.py     (refactored)
@@ -1 +1 @@
-x = input("Enter your number: ")
+x = eval(input("Enter your number: "))
RefactoringTool: Files that need to be modified:
RefactoringTool: test.py

So my guess is that it is just a little sloppy. From the Amazon description:

This is the second edition of John Zelle's Python Programming, updated for Python 3.

I think someone ran 2to3 on all of the code samples without checking the output thoroughly enough. So yes, it was a mistake to use input() in Python 2.x, and it was a mistake to use 2to3 without checking the output.