A
set
cannot contain a
list,
because a
list
is not
hashable.
And a
list
is not
hashable
because a
list
is
mutable.
s = {[5, 42]}
TypeError: unhashable type: 'list'
But a
set
can contain a
tuple,
because a
tuple
is
hashable.
And a
tuple
is
hashable
because a
tuple
is
immutable.
"""
Create and iterate through a set of tuples.
"""
import sys
corners = {
(5, 42), #Fifth Avenue & 42nd Street
(5, 34),
(1, 59),
(2, 72),
(3, 14)
}
def suffix(n):
"Return the suffix that makes the int n an ordinal number."
last2Digits = n % 100
if 11 <= last2Digits <= 13:
return "th"
lastDigit = n % 10
if lastDigit == 1:
return "st"
if lastDigit == 2:
return "nd"
if lastDigit == 3:
return "rd"
return "th" #all other numbers
for corner in corners: #Each corner is a tuple.
avenue, street = corner
print(f"{avenue}{suffix(avenue)} Avenue and {street}{suffix(street)} Street")
sys.exit(0)
2nd Avenue and 72nd Street 3rd Avenue and 14th Street 5th Avenue and 34th Street 1st Avenue and 59th Street 5th Avenue and 42nd Street
A
set
cannot contain a
set,
because a
set
is not
hashable.
And a
set
is not
hashable
because a
set
is
mutable.
s = {{5, 42}}
TypeError: unhashable type: 'set'
But a
set
can contain a
frozenset,
because a
frozenset
is
hashable.
And a
frozenset
is
hashable
because a
frozenset
is
immutable.
fs = frozenset({5, 42}) #Call the frozenset function.
s = {fs}
print(s)
{frozenset({42, 5})}
"""
Create and iterate through a set of frozensets.
"""
import sys
import itertools
alliances = {
frozenset({"United States", "United Kingdom", "Soviet Union", "France"}),
frozenset({"Germany", "Italy", "Japan"})
}
for alliance in alliances: #Each alliance is a frozenset.
print(f"An alliance of {len(alliance)} countries:")
for i, member in enumerate(alliance, start = 1):
print(f"{i} {member}")
print()
for alliance in alliances:
if {"Germany", "Japan"} <= alliance: #"is a subset of"
print("Germany and Japan are allies.")
break
else:
print("Germany and Japan are not allies.")
cheaters = set()
for t in itertools.combinations(alliances, 2): #t is a tuple containing 2 frozensets.
cheaters |= t[0] & t[1] #Add the members of t[0] & t[1] to cheaters.
if cheaters: #if cheaters is non-empty
print()
print("The following countries belong to more than one alliance:")
for cheater in cheaters:
print(cheater)
sys.exit(0)
An alliance of 4 countries: 1 United Kingdom 2 United States 3 France 4 Soviet Union An alliance of 3 countries: 1 Japan 2 Italy 3 Germany Germany and Japan are allies.
Add
"Italy"
to both alliances and see what happens.
import sys
import itertools
drugs = {
"aspirin",
"alcohol",
"marijuana",
"meth"
}
for t in itertools.combinations(drugs, 2): #t is a tuple containing 2 strings.
print(f"Testing the interaction between {t[0]} and {t[1]}.")
sys.exit(0)
There are six possible pairs of four drugs:
Testing the interaction between aspirin and meth. Testing the interaction between aspirin and marijuana. Testing the interaction between aspirin and alcohol. Testing the interaction between meth and marijuana. Testing the interaction between meth and alcohol. Testing the interaction between marijuana and alcohol.
"""
orgyplanner.py
List all the possible trios of people.
"""
import sys
import itertools
people = {
"John",
"Mary",
"Bill",
"Sue",
"Sarah"
}
for t in itertools.combinations(people, 3): #t is a tuple containing 3 strings.
print(f"{t[0]}, {t[1]}, and {t[2]}")
sys.exit(0)
There are 10 possible trios:
John, Mary, and Bill John, Mary, and Sue John, Mary, and Sarah John, Bill, and Sue John, Bill, and Sarah John, Sue, and Sarah Mary, Bill, and Sue Mary, Bill, and Sarah Mary, Sue, and Sarah Bill, Sue, and Sarah