Chapter 9: Dictionaries

Question 1

difference between dictionary and list

Answer 1

dictionary is more general - maps between a set of indicies (keys) and a set of values

Question 2

key

Answer 2

set of indicies that maps to a value

Question 3

association of a key and a value…

Answer 3

called a key-value pair, or an item

Question 4

turn eng2ger (english to german dictionary) into a dictionary

Answer 4

eng2ger=dict()

Question 5

braket type of dictionary

Answer 5

{ } - curly brackets.

Question 6

create item mapping key ‘one’ to value ‘eins’

Answer 6

eng2ger[‘one’]=’eins’

Question 7

print(eng2ger)

Answer 7

{‘one’: ‘eins’}

Question 8

add more

Answer 8

eng2ger[‘x’]=’y’, will just add new ones

Question 9

creating dict with multiple items at start

Answer 9

eng2ger={‘three’: ‘drei’, ‘four’: ‘vier’} - output can be used to create new one

Question 10

show value of a key

Answer 10

print(eng2ger[‘one’]) returns eins

Question 11

find number of items

Answer 11

len(eng2ger), returns no. of items

Question 12

‘in’ operator can be used to tell us if a…

Answer 12

key is in the dictionary, but not a value. eg

‘one’ in eng2ger #returns True, but ‘eins’ returns False

Question 13

to see if a value is in dictionary…

Answer 13

use the ‘values’ method to return a list, then use the ‘in’ operator. x=list(eng2ger.values())
‘eins’ in x #returns true

Question 14

what does c mean, as in “for c in str

Answer 14

character

Question 15

dictionary to tally characters in a string, ie give frequency of each

Answer 15

word='brontosaurus'
d=dict()
for c in word:
  if c not in d:  <
    d[c]=1          <
  else:             <
    d[c]=d[c]+1  <

print(d)

Question 16

‘get’ dictionary method

print(dic.get(‘key’, ‘value’))

Answer 16

prints the value of the key if key is present, otherwise prints the other value put in brackets

Question 17

use ‘get’ to make character tally more concise

Answer 17

word=’brontosaurus’
d=dict()
for c in word:
d[c]=d.get(c, 0)+1 <

print(d)

Question 18

x+=1
-=…
*=…
/=…

Answer 18

equiv to x=x+1 etc

Question 19

list all keys with values next to them

Answer 19

dic=…
for key in dic:
print(key, dic[key])

Question 20

‘keys’ dictionary method

Answer 20

makes a list of keys

lst=list(dic.keys()). can then be sorted, and looped through to report each key and its value

Question 21

do the same, but sorted alphabetically (via list)

Answer 21

dic=...
lst=list(dic.keys())
lst.sort()
for key in lst:
   print(key, dic[key])

Question 22

‘lower’ string method

make a line all lowercase

Answer 22

line=line.lower()

Question 23

‘punctuation’ string method

identify puntuation in a str

Answer 23

str.punctuation

Question 24

‘translate’ string method

Answer 24

not sure if important yet

Question 25

delete punctuation on a line with ‘translate’ string method

Answer 25

line=line.translate(line.maketrans(‘’, ‘’, string.punctuation))
first 2 parameters empty. deletes all of 3rd parameter (all punctuation present if it exists).

Question 26

swap keys with values in dictionary

Answer 26

d={value:key for key, value in d.items()}

Question 27

copy dictionary. NB, multiple values can be the same, keys can’t. so when reversed this well mess things up.

Answer 27

dict2=dict1.copy()

Question 28

long-winded way to avoid duplicate key problem above is in chap9ex3-4. May be able to avoid, as in chap9ex3-4_simpler

Answer 28

gives a way of identifying a value without knowing the key, and printing both