Question

For problem set 3 problem 2, how would you create the tuple? Tuples are immutable so you wouldn't be able to create a loop that adds locations to the tuple. You can't create variables of the locations of each key because you don't know how many instances there are. Please help

Answer 1

you can either use a list, and append locations to it, then make the tuple from the list, or you can have a variable that refers to the tuple and just create new tuples to add the location:

#with list
locs = []
for i in range(5):
locs.append(2*i)
print tuple(locs)

#with tuple
locs = ()
for i in range(5):
locs = locs + (3*i,)
print locs

Answer 2

Oh, so you can add to a tuple? It's called immutable so I just assumed it couldn't be changed at all once created.

Thanks polpak

Answer 3

No you cannot add to it. I thought that is what I said. You can create a new tuple whos elements are taken from another tuple though. Notice in my tuple example I'm saying:

locs = locs + (3*i,)

This creates a new tuple whos contents are taken as all the elements in locs and all the elements in the second tuple. Then it re-assigns the name locs to reference this new tuple instead of the original one.

Answer 4

Numeric data types and strings are also immutable, but that doesn't stop you from saying:
i = 5
i = i + 1
or
s = 'ham'
s = s + ' and eggs'

Because again, you're constructing a new object from other data, then re-assigning the object your name references to the new one you just created.

Answer 5

For a better understanding, consider this code:

t1 = (1,2,3)
t2 = t1

print t1, t2
print id(t1), id(t2)

t2 = t2 + (4,)

print t1, t2
print id(t1), id(t2)

# Versus

l1 = [1,2,3]
l2 = l1

print l1, l2
print id(l1), id(l2)

l2.append(4)

print l1,l2
print id(l1), id(l2)