Octber 24th, 2021
Written by Juliette Woodrow, Brahm Capoor, Nick Parlante, Anna Mistele, and John Dalloul
This week in section you will gain practice with string parsing, building lists, drawing, and the main function. These problems are meant to prepare you for homework 5. Solutions will be posted at the end of the week. There are more problems on this than we expect you to get through in section. Feel free to use the other ones as practice! If you have any questions, post on Ed or email Juliette!
We have gotten a lot of questions about why s[len(s)] causes an eror but using len(s) as the right index in a slice does not cause an error. For eaxmple:
>>> s = 'zz@python' >>> at = s.find('@') >>> end = len(s) >>> s[end] Traceback (most recent call last): File "stdin", line 1, in module IndexError: string index out of range >>> >>> s[at + 1:end] 'python'
What is going on here? There are two reasons why this happens.
Reason 1: UBNI
Reason 2: Slice Garbage
>>> s = 'Python' >>> len(s) 6 >>> s[2:5] 'tho' >>> s[2:6] 'thon' >>> s[2:46789] 'thon'
Implement a function, find_time(str) that takes in a string and, if it contains one, returns a time written in the string. Times will be of the format "XX:XX" and you don't need to include any AM or PM designations. For example, given the input string "Let's go to the movies at 09:30 tomorrow" your function should return "09:30". If there are no times in the string, return the empty string.
Implement a function, parse_out_hashtag(s), which takes in a string representing a single tweet and returns the hashtag within the tweet. For this problem, each tweet will have only one hashtag. A Hashtag can be defined as a string of 1 or more alphanumeric characters immadiately following a "#" character. A single hashtag ends at the first non-alphanumeric character following the '#'. For example, parse_out_hashtag('I am going to #wearmymask everywhere') would return 'wearmymask' and parse_out_hashtag('what is #ResX?') would return 'ResX'.
Here are some drawings for looping over the word following the '#' character (also known as an octothorpe).
Implement a function, find_price(s, currency) that takes in a string and a currency symbol and returns an integer price if that is mentioned in the string s. We want to look through a line and find the place where a price is mentioned. You can assume that the currency symbol specified will only show up once in the line provided. To find the price, locate the currency symbol and then find all the digits AFTER the symbol (not all currencies have the symbol come first--think about how we could adjust our code if the symbol came last, instead). Stop reading once the last digit has been read. Return the price as an integer (without the currency symbol).
For example, find_price("Une cramique au chocolat coûte €3", "€") would return 3.
Implement a function, exclaim_word(s), which takes in a string and returns the exclamatory word in that string. Consider an exclamatory word the "word" substring of one or more alphabetic chars which are immediately to the left of the '!' in s. For example: exclaim_word('x123hello!cs106a') would return 'hello' and exclaim_word(32happy!day') would return 'happy'. If there are no exclamatory words, return the empty string.
Implement a function, parse_phone_number(s), which takes in a string that has a ten digit phone number somewhere in it and returns a list of the number in two parts: the area code and the rest of the number. The area code is the part of the phone number up until the first '-' character. The string can have text before or after the phone number. You may assume the following: that the only digits in the string will be part of the phone number. If there are any digits in the string, they will make up a complete phone number. If there is no phone number in the string, return an empty list. There may be '-' outside of the phone number. For example, parse_phone_number('Zoom is too much-call me instead: 212-225-9876') would return ['212', '2259876'], parse_phone_number('so call-me beep-me if you wanna reach me-at 650-555-5555 ') would return ['650', '5555555'], and parse_phone_number('The weekend is not long enough') would return .
You have been hired by Stanford to create a digital version of their new flag that they are desiging to welcome all students back to campus in the fall. They have given you the following description of the flag:
To accomplish this task, decompose into a function called draw_stanford_flag(canvas, left, top, width, height, num_stripes) where left should be the starting x value of the top left corner of this flag on the canvas and top should be the starting y value of the top left corner of this flag on the canvas.
You should also decompose into a function called draw_spider_patch(canvas, left, top, width, height, n) where left should be the starting x value of the top left corner of this spider patch on the canvas and top should be the starting y value of the top left corner of this spider patch on the canvas. n is the number of lines to draw and is guaranteed to be 2 or more.
Once you have that working, write a function called draw_flag(canvas, width, height, num_stripes, n) which draws the three flags at their locations specified above. Below is an example of what one call to draw_flag(canvas, 600, 600, 9, 4) should look like. You can ignore the black outline on parts of the image.
Your job is to write a program that emulates the 3 calculator functions shown below:
You may assume that you are provided with a main function that takes as a parameter the list of arguments typed in the console, as below:
$ python3 calculator.py -square 42 1764 # prints the square of the number passed in $ python3 calculator.py -exp 2 10 1024 # prints the first number raised to the power of the second number $ python3 calculator.py -add 1 2 3 4 5 15 # prints the sum of all the numbers typed in
Thus, your job is to decompose and implement the main function so that your program produces the sample output above.
import sys def main(args): # your code here pass if __name__ == "__main__": main(sys.argv)