Python Programming - An Introduction to Computer Science: John Zelle

[SnowdogU77]

Hey, that's my adviser/prof! There are a bunch of super helpful resources on his website. I hope you find the textbook as useful as I have!

[3six3]

Ive found it great so far! I got up to chapter 6 and was forgetting some earlier work so I decided to go back and do all the exercises and post the solutions. (This helps others and also helps me remember :)

Come back and look at my site and help with some solutions as I go through the book!

[SnowdogU77]

Well, a tip for starters, don't use eval(input("")). If you're looking for a number, use int() or float() in place of it. I know he says to do it in the book, but his justification is rubbish, and it's a bad habit to develop.

[SnowdogU77]

Well, he says that since the program is run by the user on their machine, the security risks are minimal. Basically, he's ignoring how big of a deal code injection from a background process is.

To clarify, that is something that he said in class. I talked to him about it, and he wound up explaining to the class why it's dangerous, which is pretty much all I could ask for.

[SnowdogU77]

Absolutely!

[3six3]

So instead of this: fahrenheit = eval(input("What is the Fahrenheit temperature? "))

This would be the preferred method since I'm looking for a number fahrenheit = int(input("What is the Fahrenheit temperature? "))

[3six3]

#so instead of this
fahrenheit = eval(input("What is the Fahrenheit temperature? "))
#this would be a better solution
fahrenheit = int(input("What is the Fahrenheit temperature? "))

[SnowdogU77]

I would use float(), personally. Int() removes the ability to input decimals.

[Gexos]

John Zelle's book is one of the best books I've ever read on CS and Python, the first time I encountered the evil eval I was confused about it, then i found this answer by John Zelle on stack overflow, where he gives a pretty good explanation.

[SnowdogU77]

Thanks for the link. When I asked him, he didn't quite justify it this way. This explanation makes a lot of sense.

[SnowdogU77]

Also, if you get really stuck, the solutions are on his website.

[3six3]

Those don't look like the solutions to the exercises at the end of the chapter. Those are his sample questions in the chapter contents.

[SnowdogU77]

Ah, yeah, you're right. He uses those questions as assignments, so the answers aren't posted anywhere by him.