I have a small class that creates a building. I am wanting to learn more about iter. The following works:
class Building(object):
def __init__(self, floors):
self._floors = [None] * floors
def __setitem__(self, floor_number, data):
self._floors[floor_number] = data
def __getitem__(self, floor_number):
return self._floors[floor_number]
def __iter__(self):
for floor_number in self._floors:
yield self._floors[floor_number]
building1 = Building(9) # Construct a building with 9 floors
building1[0] = 'Reception'
building1[1] = 'ABC Corp'
building1[2] = 'DEF Inc'
building1[3] = 'Apple'
building1[4] = 'Cisco'
building1[5] = 'Microsoft'
building1[6] = 'Dell'
building1[7] = 'EMC'
building1[8] = 'HPE'
'''
for floor in building1:
print(building1[floor])
'''
print(building1[6])
Dell
But if I un-comment out the for loop I get this:
Traceback (most recent call last):
File "C:/Users/Mark/PycharmProjects/main/main.py", line 28, in <module>
for floor in building1:
File "C:/Users/Mark/PycharmProjects/main/main.py", line 13, in __iter__
yield self._floors[floor_number]
TypeError: list indices must be integers or slices, not str
I understand that list indices have to be integers. What I am not getting is why this for loop is violating that restriction.
What I am wanting to do is exercise the iter protocol and print out every floor in the building, not just a specific one.
You misunderstood what a for
loop does; you don't have indices, you have your actual values in the list. Just yield those:
for contents in self._floors:
yield contents
You need to do the same in your outer loop:
for contents in building1:
print(contents)
Python for
loops are Foreach loops, you iterate over the values, not an index.
Instead of looping, your __iter__
method could just return an iterator for the list, effectively delegating to the list iterator that iter()
produces for you:
def __iter__(self):
return iter(self._floors)
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