Quiz 4 Material

Question 1

Is repetition of items allowed in dictionaries?

Answer 1

no

Question 2

Is indexing a dictionary the same as indexing a list? if no, what do you use instead?

Answer 2

you index with keys instead

Question 3

dictionaries consist of _____-______ pairs

Answer 3

key-value

Question 4

how would you add something to a dictionary?

Answer 4

d[key] = value

Question 5

how would you delete something from a dictionary?

Answer 5

del d[key]

Question 6

what would the len(d) give us?

Answer 6

how many key-value pairs are in the dictionary

Question 7

what will each of these do?

dict_name.copy()
dict_name.keys()
dict_name.values()
dict_name.items

Answer 7

• creates a copy of the dictionary
• returns set of key values in the dictionary
• returns set of values in dictionary
• returns set of (key, value) pairs in the dictionary

Question 8

what will each of these do?

list(dict_name)
key in dict_name
dict_name.popitem()
dict_name.pop(key[,default)
dict_name.get(key[, default)

Answer 8

• returns a list of all the keys in the dictionary
• returns True if dictionary has a key: key, else False
• remove and return a (key, value) pair from the dictionary
• if key is in the dictionary, remove it and return its value, else return default. if default is not given and key is not in the dictionary, a KeyError is raised
• return the value for key if it is in the dictionary, else default. if default is not given, it defaults to None, so it doesn’t raise a KeyError

Question 9

what will this return?

str1 = ‘Have a nice day’
x = str1.split()

Answer 9

[‘Have’, ‘a’, ‘nice’, ‘day’]
(we can also pass in a argument to split the string into something other than the whitespace)

Question 10

what will each of these return?

x,y = 4,7
print(y)

numbers = [1,2,3,4,5]
a,b,c,d,e = numbers
print(d)

Answer 10

print(y): 7
print(d): 4

Question 11

what does this return?
my_list = [[8,6,7],[5,3,0,9]]
print(my_list[1][0])

Answer 11

5

Question 12

color_str = ‘red,orange,yellow,green,blue,purple’
color_list = color_str.split()
print(color_list[0])

Answer 12

red,orange,yellow,green,blue,purple

Question 13

color_str = ‘red,orange,yellow,green,blue,purple’
color_list = color_str.split(‘,’)
print(color_list[0])

Answer 13

red

Question 14

steps to reading a file

Answer 14

1. tell python to read from
2. python sends it and your OS gives back a readable ‘stream’
3. read the data from the stream (line-by-line or all at once)
4. streams are always read-once
5. close the file when you are done with it

Question 15

what are the 2 ways to open a file?

Answer 15

file_connector = open(filename,’r’)

with open(filename, ‘r’) as a file_connector

Question 16

what are the 2 ways to read a file line-by-line?

Answer 16

file_connector.readline() – the next unread line

for line in file_connector – the variable line will contain the next unread line each time through the loop

Question 17

what is the difference between file_connector.read() and file_connector.readlines()

Answer 17

• returns one string representing the entire file
• returns a list of all the remaining lines as strings

Question 18

what does urllib.request.urlopen(url) do?

Answer 18

open a web file to be read

Question 19

steps for reading from a web file

Answer 19

1. import urllib.request
2. open the web file usingurllib.request.urlopen(url)
3. f.read().decode(‘utf-8’) OR f.readline().decode(‘utf-8’) OR f.readlines.decode(‘utf-8’) OR
   for line in f:
   line = line.decode(‘utf-8)