Assign image array to string

Question

I want to assign my image names to another string. Below I have described the problem.

num=[10,20,30,40,50,60,.....500]
for i in range(len(num)):
  img[i]=str(num[i])+'_image_plane_XX_YY.fits'

so after this loop it should give me,

img0='10_image_plane_XX_YY.fits'
img1='20_image_plane_XX_YY.fits'
....
img499='500_image_plane_XX_YY.fits'

this means, img0 equal the image name of 10_image_plane_XX_YY.fits, img1 equal the image name of 20_image_plane_XX_YY.fits, etc. So I just need to use img0, img1,..for my corresponding images in further analysis. But, when I run this loop, it gives me following error

TypeError: 'str' object does not support item assignment

Please let me know any sollution for this.

Thanks in advance!

Cheers,

-Viral

rchang · Accepted Answer · 2015-03-03 11:22:04Z

2

For what I think you are trying to do, a list comprehension seems like the more natural approach.

num=[10,20,30,40,50,60]  # I truncated your array for brevity
img = [str(i)+'_image_plane_XX_YY.fits' for i in num]

This will construct img as an array with your assembled strings. For example:

>>> num=[10,20,30,40,50,60]
>>> img = [str(i)+'_image_plane_XX_YY.fits' for i in num]
>>> img[0]
'10_image_plane_XX_YY.fits'
>>> img[3]
'40_image_plane_XX_YY.fits'

answered Mar 3, 2015 at 11:22

rchang

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1 Comment

physics_for_all Over a year ago

Thanks rchang. That's exactly what I wanted.

laike9m · Accepted Answer · 2015-03-03 11:18:24Z

0

There's only one reason for this: your img is a string.

This err msg means: strings are immutable, so you can't change their characters in-place.

I think you img should be a list or something similar. Plz check your code.

answered Mar 3, 2015 at 11:18

laike9m

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Comments

Community · Accepted Answer · 2017-05-23 11:50:50Z

0

The problem is in img[i], since you're trying to assign a string to string index and - as the error tells you - strings don't support item assignment.

You can use a dict instead:

img = {}
num=[10,20,30,40,50,60,.....500]
for i in range(len(num)):
   img[i]=str(num[i])+'_image_plane_XX_YY.fits'

So that img becomes:

{ 0:'10_image_plane_XX_YY.fits', 
  1: '20_image_plane_XX_YY.fits',
  ....
  499: '500_image_plane_XX_YY.fits'
}

and you can call images name as:

>>> img[0]
'10_image_plane_XX_YY.fits'

>>> img[1]
'20_image_plane_XX_YY.fits'

However, if you don't need anything other than an integer as key, you should probably use list comprehension as suggested by rchang.

edited May 23, 2017 at 11:50

CommunityBot

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answered Mar 3, 2015 at 11:27

Railslide

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