multi-level sorting
here’s a list of fruits and their prices:
prices = {
'apple' : 20,
'melon' : 7,
'peach' : 20,
'grapes' : 25,
'watermelon' : 5,
'apricot' : 7,
'citrus' : 5
}
fruits_in_store = list(prices.keys())
can you use the function sorted to fruits_in_store first by price and then by alphabetical order?
### useful
prices = {
'apple' : 20,
'melon' : 7,
'peach' : 20,
'grapes' : 25,
'watermelon' : 5,
'apricot' : 7,
'citrus' : 5
}
fruits_in_store = list(prices.keys())
# solution 1
def getprice(fruit):
return prices[fruit]
def price_and_name(fruit):
return (prices[fruit], fruit)
sorted(fruits_in_store, key=price_and_name)
# solution 2
def identity(fruit):
return fruit
def make_sorter(key_funcs):
def sort_key(fruit):
return tuple(key(fruit) for key in key_funcs)
return sort_key
sorted(fruits_in_store, key=make_sorter([len, getprice, identity]))
count repeating words in a song
Count the number of times each word appears in this short song
song = """\
Lovely Spam! Wonderful Spam!
Lovely Spam! Wonderful Spam
Spa-a-a-a-a-a-a-am
Spa-a-a-a-a-a-a-am
Spa-a-a-a-a-a-a-am
Spa-a-a-a-a-a-a-am
Lovely Spam! (Lovely Spam!)
Lovely Spam! (Lovely Spam!)
Lovely Spam!
Spam, Spam, Spam, Spam!
"""
you may find certain classes in the module collections useful
song = """\
Lovely Spam! Wonderful Spam!
Lovely Spam! Wonderful Spam
Spa-a-a-a-a-a-a-am
Spa-a-a-a-a-a-a-am
Spa-a-a-a-a-a-a-am
Spa-a-a-a-a-a-a-am
Lovely Spam! (Lovely Spam!)
Lovely Spam! (Lovely Spam!)
Lovely Spam!
Spam, Spam, Spam, Spam!
"""
song = song.translate(song.maketrans('', '', ',.!()')) # remove annoying chars
words = song.split()
from pprint import pprint
def order_by_value(d):
return dict(sorted(d.items(), key=lambda item: (item[1], item[0]), reverse=True))
# solution #1
counter = {}
for word in words:
if word not in counter:
counter[word] = 1
else:
counter[word] +=1
pprint(order_by_value(counter))
print()
# solution #2
counter = {}
for word in words:
counter[word] = 1+ counter.get(word, 0)
pprint(order_by_value(counter))
print()
# solution #3
import collections
counter = collections.defaultdict(int)
for word in words:
counter[word] +=1
pprint(order_by_value(counter))
print()
# solution #4
counter = collections.Counter(words)
pprint(order_by_value(counter))
print()
file read generator
how is it that we can iterate over lines in a file with a for loop? in this exercize we will write a generator function that shows how this works in practice.
write a function called def make_file_reader(f): that can be used in the following manner:
for line in make_file_reader(open('spam.txt')):
print(line)
the make_file_reader function should take very little time/memory to run,
regardless of how big the file is. the file could potentially be 1000GB or more and still take only milliseconds to run.
you are only allowed to use the function f.readline() on file objects.
def make_file_reader(f):
line = None
while line != "":
line = f.readline()
yield line
### useful test for your make_file_reader()
with open('spam.txt', 'w') as f: print(song, file=f)
for line in make_file_reader(open('spam.txt')):
print(line, end='')