Python Basics

Lab Ground Rules

Important: Read Lab Ground Rules in the resources page.

[30pts] Part 1: Shopping Cart

Tips

Python supports if-statements and while-loops. Feel free to use them. Check the documentation.
If you want to exit the entire program, you can use exit(0).
When open() fails, an OSError exception will be raised. Check the documentation.
You will probably need to call split() many times.
You can use an in operation to see if a keyword is in a given dictionary.

Your task

Write a program p1.py that

reads in a data file containing fruit name/price-per-pound pairs (e.g. fruit1.txt, fruit2.txt)
note: If the file can't be opened, the program should print the message File not found! and exit.
reads and executes the following commands:
- add amt lbs name — which adds amt lbs of fruit name to the current order
  Note: if the name is not one of the ones read from the file, print the error message: Error! name not found!
- price name — which prints the price of the fruit name formatted as in this example: blueberries are $1.59 per pound
  Note: if the name is not one of the ones read from the file, print the error message: Error! name not found!
- checkout — which exits the program, printing out the total price of the order in the format: total is $num

Assume the user always enters a valid command from the three above.

Sample Runs

~/$ python3 p1.py
Filename: fruit1.txt
command: add 3 lbs mango
command: price asdf
Error! asdf not found!
command: price peaches
Error! peaches not found!
command: price blueberries
blueberries are $1.59 per pound
command: add 2.1 lbs blueberries
command: checkout
total is $5.469

~/$ python3 p1.py
Filename: fruit2.txt
command: add 2.0 lbs oranges
command: price kiwi
kiwi are $1.07 per pound
command: price starfruit
Error! starfruit not found!
command: add 1.5 lbs peas
Error! peas not found!
command: add 1.5 lbs plums
command: checkout
total is $2.505

~/$ python3 p1.py
Filename: foobar.txt
File not found!

Note:

You must pass all the testcases in the submit server.

[30pts] Part 2: Hexdump

hexdump a useful utility program that shows the contents of a file in binary and text form.

Download ex1_test.py and two.pcap.

$ cat ex1_test.py
from ex1 import *
a = 0b11010101
pr(a)
b = zero_out_top(a, 3)
pr(b)
c = set_one_at(a, 2)
pr(c)
d = set_zero_at(a, 1)
pr(d)

$ hexdump -C ex1_test.py
00000000  66 72 6f 6d 20 65 78 31  20 69 6d 70 6f 72 74 20  |from ex1 import |
00000010  2a 0a 61 20 3d 20 30 62  31 31 30 31 30 31 30 31  |*.a = 0b11010101|
00000020  0a 70 72 28 61 29 0a 62  20 3d 20 7a 65 72 6f 5f  |.pr(a).b = zero_|
00000030  6f 75 74 5f 74 6f 70 28  61 2c 20 33 29 0a 70 72  |out_top(a, 3).pr|
00000040  28 62 29 0a 63 20 3d 20  73 65 74 5f 6f 6e 65 5f  |(b).c = set_one_|
00000050  61 74 28 61 2c 20 32 29  0a 70 72 28 63 29 0a 64  |at(a, 2).pr(c).d|
00000060  20 3d 20 73 65 74 5f 7a  65 72 6f 5f 61 74 28 61  | = set_zero_at(a|
00000070  2c 20 31 29 0a 70 72 28  64 29 0a 0a 0a           |, 1).pr(d)...|
0000007d

The first column is the location of the data in a hexadecimal form. Since each line shows 16 bytes, the first column increases by 16 (i.e., 0x10). The last line (0x7d) shows the actual size of the file.
The second column shows the data contents in a hexadecimal form.
The last colum shows the data contents in pritable format. If a given data byte is not printable, it simply prints ".".

Your task

Write p2.py that exactly does what hexdump does. A sample run:

$ python3 p2.py ex1_test.py
00000000  66 72 6f 6d 20 65 78 31  20 69 6d 70 6f 72 74 20  |from ex1 import |
00000010  2a 0a 61 20 3d 20 30 62  31 31 30 31 30 31 30 31  |*.a = 0b11010101|
00000020  0a 70 72 28 61 29 0a 62  20 3d 20 7a 65 72 6f 5f  |.pr(a).b = zero_|
00000030  6f 75 74 5f 74 6f 70 28  61 2c 20 33 29 0a 70 72  |out_top(a, 3).pr|
00000040  28 62 29 0a 63 20 3d 20  73 65 74 5f 6f 6e 65 5f  |(b).c = set_one_|
00000050  61 74 28 61 2c 20 32 29  0a 70 72 28 63 29 0a 64  |at(a, 2).pr(c).d|
00000060  20 3d 20 73 65 74 5f 7a  65 72 6f 5f 61 74 28 61  | = set_zero_at(a|
00000070  2c 20 31 29 0a 70 72 28  64 29 0a 0a 0a           |, 1).pr(d)...|
0000007d

Tips

Read the file in binary format and read the whole data into a bytes object.
Note each element of a bytes object is an integer (ASCII code).
Deal with each ASCII code one by one.
- How do you print a number in a hex format?
- What is a function that converts an ASCII code to a string?
You will probably need to use str.isprintable() function to determine if you should put '.' instead of the actual string. See here.
You may need to be careful to use the end option in print().

[30pts] Part 3: Bit manipulations

Write a program p3.py so that the following code works as follows.

>>> from p3 import *
>>> a = 0b10110101
>>> pr(a)
dec: 181
hex: 0xb5
bin: 10110101
>>> b = zero_out_top(a,3)
>>> pr(b)
dec: 21
hex: 0x15
bin: 00010101
>>> c = set_one_at(a, 4)
>>> pr(c)
dec: 189
hex: 0xbd
bin: 10111101
>>> d = set_zero_at(c, 4)
>>> pr(d)
dec: 181
hex: 0xb5
bin: 10110101

Warning: No strings! No loops!

The purpose of this part is learning how to manipulate bits. You are not allowed to use strings or loops in this part.

You will get 0 point:

If you use any string (except using format strings like f"..." in the function pr()).
If you use any loop.

Other requirements

The code only needs to work with 8-bit numbers.
Note that p3.py should provide the following functions:
- pr(): Similar to the above. Make sure it always prints 8 bits.
- zero_out_top(a, n): Outputs a number where top n bits are zeroed out from a.
- set_one_at(a, i): Outputs a number where the ith bit of a is set to 1. The index goes from left to right, starting with 0.
- set_zero_at(a, i): Outputs a number where the ith bit of a is set to 0.

You may want to save time for debugging by creating a test python file as follows:

# p3_test.py
from p3 import *
a = 0b10110101
pr(a)
b = zero_out_top(a,3)
pr(b)
c = set_one_at(a, 4)
pr(c)
d = set_zero_at(c, 4)
pr(d)

[10pts] Lab Report and Submission

Write a lab report by using the provided template. The writing quality of the lab report matters.

~/bin/submit -c=IT430 -p=lab01 *.py lab01.docx

NOTE:

In this lab, you don't need to describe your solutions. Just give the first page material of the lab report (i.e., challenges, learning points, and interesting points).
You need to make sure to pass the test cases in the submit server. For easier grading, each student should submit the full code to the submit server.