Python Basics Quiz: Interpreter, Console I/O and Tracebacks

Instructions

This checkpoint covers the whole module: what CPython is and how it runs a file, the four ways to run Python and the __name__ guard, the parts of a program (statements, expressions, blocks, comments, docstrings, names), the console I/O patterns every exercise uses, and how to read a syntax error and a traceback.

How it works. Twelve questions and three programs. You need 70% on the questions and every program accepted to clear the module. You can retake it as often as you like; your best score counts.

Before you start, make sure you can answer these from memory:

• What does CPython do with your source before the first line runs, and what stops it?
• When is __name__ equal to "__main__", and why does a script check?
• What does input() return, what does it strip, and what does it raise at the end of input?
• How do you print the elements of a list separated by spaces, and why is print(nums) wrong?
• Which exit code means success, and what does an uncaught exception do to it?
• In a traceback, which line says what went wrong and which says where?
• What is the difference between TypeError and ValueError?

The three programs are a receipt built from records read line by line and printed with fixed decimals, a calculator that reports the exception name instead of crashing, and a word-count utility that reads standard input to the end.

Common questions

What does input() return, and what does it raise at the end of input?

input() returns one line of standard input as a string, with the trailing newline stripped — digits included, so int(input()) is needed for a number. When there is no more input it raises EOFError, which a read-until-end loop catches.

What does an uncaught exception do to a Python program's exit code?

It ends the program with exit code 1 after printing a traceback to standard error. Exit code 0 means success, and it is what a script returns when it reaches the end of the file normally.

In a Python traceback, which line says what went wrong and which says where?

The last line says what: the exception type and its message. The frame just above it says where: the file, line number and function that raised it. The frames above that are the callers that led there, most recent call last.

Exercises

2
apple 3 0.5
bread 1 2.25

apple x3 @ 0.50 = 1.50
bread x1 @ 2.25 = 2.25
total = 3.75

7 + 2
7 / 2
7 // 0
7 ^ 2

9
3.50
ZeroDivisionError
ValueError

hello world
foo

lines 2
words 3
chars 16

In this module: Python and the interpreter

• What Python is, and why it looks the way it does
• Running Python — the REPL, scripts, modules and the judge
• Anatomy of a Python program
• Console input and output — the patterns every exercise uses
• Errors and tracebacks — reading what the interpreter tells you
• Checkpoint — Python and the interpreter (this lesson)