Class 7 - Notes

Upcoming Schedule

Due now: Project 1
Before Wednesday, 10 February:
    Complete Udacity cs101 Lesson 3: How to Manage Data (Notes) and Lesson 3: Problem Set
Due on Monday, 15 February:
    Project 2 (will be posted in a few days)
Before Friday, 19 February:
    Udacity cs101 Lesson 4: Responding to Queries (Notes) and Lesson 4: Problem Set

Python Tutor

One great resource for understanding python code is Philip Guo’s Python Tutor. It lets you step through Python code forwards and backwards, and visualize what is going on.

Slides

Binary Numbers and Rules of Evaluation

Binary numbers are base 2, instead of the base 10 decimal numbers we commonly use. This means we can represent any number using only 0s and 1s, and the value of each Bit scales as a power of two (so instead of having a "ones" place, "tens" place, "hundreds" place, "thousands" place, we have a "ones" place", "twos" place, "fours" place, "eights" place, etc.). In Python, a number literal that starts with 0b is interpreted as a binary number:

>>> 0b10
2
>>> 0b101
5
>>> 0b1120
SyntaxError: invalid syntax

What is the value of 0b11111111 (as a decimal number)?

Show how to derive 0b101 with this grammar starting with IntegerLiteral:

Provide semantic rules for the grammar that give the value (as a decimal number) for every BinaryLiteral:

Test Grammar

Here is a simplified excerpt of the Test grammar from https://docs.python.org/3/reference/grammar.html.

0x11 < 0x011
True and False and True
0b11 < 0b100 > 0b101  
not not not not not not False
not not not
not False and True

Develop rules of evaluation for the grammar above that matches how things are interpreted by the Python interpreter.