My main issue is with printing the index in the following situations.

catNames = []
while True:
    print('Enter the name of cat '   str(len(catNames) 1)   ' (or enter nothing to stop.):')
    name = input()
    if name == '':
        break
    catNames = catNames   [name]
print('The cat names are:')
for name in catNames:
    print(str(catNames.index(name) 1)   '. '   name)

In this first scenario, the results are

Enter the name of cat 1 (or enter nothing to stop.):
george
Enter the name of cat 2 (or enter nothing to stop.):
sally
Enter the name of cat 3 (or enter nothing to stop.):
chloe
Enter the name of cat 4 (or enter nothing to stop.):

The cat names are:
1. george
2. sally
3. chloe

Which is exactly as expected.

However, when I try this for another scenario, it doesn't work. The next example is as below:

supplies = ['pens', 'staplers', 'flamethrowers', 'binders']
for i in supplies:
    print('Index '   str(supplies.index(i) 1)   'in supplies is: '   supplies[i])

I instead get the error stating "TypeError: list indices must be integers or slices, not str".

I understand there's a better way to express the supplies example using range(len(supplies) but I'm just keen to understand why using the for i in supplies version doesn't work, although it worked for catNames. Thanks!

CodePudding user response：

You're doing well here

for name in catNames:
    print(str(catNames.index(name) 1)   '. '   name)

You're doing different here by using supplies[i]

for i in supplies:
    print('Index '   str(supplies.index(i) 1)   'in supplies is: '   supplies[i])

Solution

do the same as when it worked

for i in supplies:
    print('Index '   str(supplies.index(i) 1)   'in supplies is: '   i)

Improve

Use enumerate to yields the current index while iterating, you can even choose the starting value

for idx, supply in enumerate(supply, 1):
    print('Index '   idx   'in supplies is: '   supply)

CodePudding user response：

"TypeError: list indices must be integers or slices, not str".
the place where it happens: supplies[i]
supplies = ['pens', 'staplers', 'flamethrowers', 'binders']
i = pens (for example)
so with this line supplies[i] you try to do thissupplies[pens]

list idx must be like [::-1] or [0] not str, not 'pens'

p.s. the best way to do it is enumerate:

supplies = ['pens', 'staplers', 'flamethrowers', 'binders']
for idx,i in enumerate(supplies):
    print(f'Index {idx} in supplies is: {i}')

# Index 0 in supplies is: pens
# Index 1 in supplies is: staplers
# Index 2 in supplies is: flamethrowers
# Index 3 in supplies is: binders