Sep 14, 2020 Notes

IT 212 -- Sep 14, 2020

Review Exercises

Zoom Poll 1 Review Exercises questions and answers. Correct answers are marked with *:
1. For questions 1 to ?, which of the following are legal Python local variable names? Recall that a variable name must start with a lower case letter or underscore. The remaining characters must be letters, digits, or underscores.
  The python variable name is total_value
  *a. Legal b. Not legal
2. total value
  a. Legal *b. Not legal
  Explanation: no embedded blanks allowed.
3. totalValue
  *a. Legal b. Not legal
  Explanation: Camel casing is allowed in Python, but the class examples will use underscore notation.
4. TotalValue
  a. Legal *b. Not legal
  Explanation: Local variable names must start with a lower case letter. User defined class names start with an uppercase letter, so TotalValue would be a good class name.
5. total value
  a. Legal *b. Not legal
  Explanation: an embedded minus sign or dash is not one of the allowed characters for a Python variable name.
6. i2
  *a. Legal b. Not legal
  Explanation: i2 starts with a letter and the digit 2 is allowed for the second character.
7. 2i
  a. Legal *b. Not legal
  Explanation: A digit is not allowed as the first character of a variable name.
8. hook&ladder
  a. Legal *b. Not legal
  Explanation: & is not allowed in a Python variable name.
9. _
  a. Legal *b. Not legal
  Explanation: A single underscore is allowed for a variable name but is not recommended because it is hard to read.
10. an_extremely_long_identifier_if_you_ask_me
  *a. Legal b. Not legal
  Explanation: Although variable names of any length are legal, variable names longer than 10 or 12 characters are hard to read.
Zoom Poll 2 Review Exercises questions and answers:
1. What is the output of this script?
```
val1 = 4
val2 = 1.237
val3 = "dog"
print("{0:4d} {1:5.2f} {2:s}".format( 
    val1, val2, str(val1 + val2) + val3))
```
  *a. 4 1.24 41.237dog
  b. 4 1.24 5.237dog
  c. 4 1.24 41.237 dog
  d. 4 1.24 5.237 dog
2. What is the output of this script?
```
n = 13
print("{0:03d} {1:x} {2:02x} {3:08b}".format( _
    n, n, n, n)
```
  a. 00001101 0d d 013 b. d 013 00001101 0d
  c. 0d 013 d 00001101 *d. 013 d 0d 00001101
3. What is a bit?
  a. One of the bool values True or False.
  *b. A binary digit.
  c. A decimal digit.
  d. A base 64 digit.
4. What is a byte?
  a. Two binary digits b. Four binary digits
  c. Six binary digits *d. Eight binary digits
5. How many bits are required to represent a hex digit?
  a. 2 *b. 4 c. 6 d. 8
6. Convert the binary value 01101111 to hex and decimal.
  a. 6d 109 b. 6f 109 *c. 6f 111 d. 615 111
7. Convert the hex value 7a to binary and decimal.
  *a. 01111010 122 b. 11101010 122
  c. 01111000 710 d. 11101000 710
8. Convert the decimal value 117 to binary and hex.
  a. 01010101 55 b. 01010111 57
  *c. 01110101 75 d. 01110111 77
Write a script that creates this list:
```
25  81  95  15
```
a. a = 25 81 95 15 b. a = 25, 81, 95, 15
c. a = [25 81 95 15] *d. a = [25, 81, 95, 15]

Write Python scripts to verify your answers for the review exercises 2f, 2g, and 2h. Ans:

# Problem 6
a = 0b01101101
print("{0:d} {1:02x}".format(a, a))

# Problem 7
b = 0x6d
print("{0:08b} {1:d}".format(b, b))

# Problem 8
c = 117
print("{0:08b} {1:02x}".format(c, c))

# Output:
01110101 75
109 6d
01101101 109

# You can also omit the argument numbers like this:
print("{:d} {:02x}".format(a, a))
print("{:08b} {:d}".format(b, b))
print("{:08b} {:02x}".format(c, c))

Bitwise Operations

Binary and Hex Numbers, Section 5: Bitwise Operations.
We looked at sections 1 through 5 on Monday.

Practice Problems:

Compute the bitwise and of 00001011 and 00001101. Write a Python script to check your answer. Also print the answer in hex and decimal.

value1 = 0b00001011
value2 = 0b00001101
bitwise_and = value1 & value2
print("{0:08b} {1:02x} {2:d}".format(bitwise_and, _
    bitwise_and, bitwise_and))

# Output:
00001001 09 9

Predict the output:

# The prefixes 0b and 0x denote binary and
# hex constants, respectively.
a = 0x5c
b = 110
print("{0:d} {1:02x} {2:08b}". 
    format(a | b, a & b, a ^ b))

# Output:
126 4c 00110010

If you are interested, read Section 6: Representing Negative Numbers in Binary. It describes the twos-complement method of representing binary numbers, which is faster and more efficient that maintaining a separate sign to distinguish between negative and positive numbers.

Project 1

Look at the Project 1 Description.
Practice Problem for Problem 5: Interpret this hex dump, where the meanings of the fields are are shown in the Project 1 description:
```
00000 41 6c 69 63 65 20 20 20 55 67 5c
       A  l  i  c  e           U  g  \
```
Interpretation: Field 1: Name is Alice (String), 3 bits for padding.
Field 2: ID is 5567 (Packed Decimal)
Field 3: Quiz scores are FTFTF (binary), 3 padding bits are 111.
The hex numbers for the letters in "Alice" are called ASCII (American Standard Code for Information Interchange) character codes.
Here are two tables of ASCII character codes: one table for printable characters; one for non-printable characters.
The Python standalone method chr returns a character, given its ASCII code.
```
chr(0x2a)   # Output: *
```
The Python function method ord returns an ASCII code, given its character
```
ord("*")    # Output: 42
```

Traditional Testing

A traditional test calls methods and prints their return values. The output is inspected to check that the return values are as expected.
Write traditional tests for three standalone methods and three str methods in this Built in Classes and Methods reference.

Here is a traditional test script for the standalone methods round, type, min, len:

# Test standalone method round:
x = 3.6556765
print(round(x, 3))
# Output: 3656

# Test standalone method type:
s = "dog"
print(type(s))
# Output: <class 'str'>

# Test standalone method min:
print(min(3, 1))
# Output: 1

# Test standalong method len:
# The string s is defined above.
print(len(s))
# Output: 3