Array won't assign more than 8 characters in python

Question

Array is acting weirdly, I have this code:

a=np.array(['dfdfdfdf', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'])

And I did this:

a[0]="hello there my friend"

Result was:

array(['hello th', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'],
      dtype='<U8')

What exactly is going on?

@knh190 actually, it's unicode, so the itemsize is 8*4 bytes, or 32 — juanpa.arrivillaga, May 23 '19 at 08:33
@JohnSall you can set a larger size for your dtype, or use `object` dtype, but why do you want to use a `numpy.ndarray` anyway? Why not just a regular `list`? — juanpa.arrivillaga, May 23 '19 at 08:33
The official doc about [dtype](https://docs.scipy.org/doc/numpy/reference/generated/numpy.dtype.html) will help. — knh190, May 23 '19 at 08:36

yatu · Answer 1 · 2019-05-23T08:39:28.067

The default dtype of an array of strings will be calculated based on the string with maximum length. In your case dtype='<U8'.

You'd have to define the dtype according to the length of the new string that you want to insert into the array.

You could do something like:

s = np.array(["hello there my friend"])
a = np.array(['dfdfdfdf', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'], \
              dtype=s.dtype) 

a[0] = "hello there my friend"

print(a)
array(['hello there my friend', 'gulf', 'egypt', 'hijazi a', 'gulf',
   'egypt'], dtype='<U21')

score 1 · Answer 2 · answered May 23 '19 at 08:34

1

Read this.

a=np.array(['dfdfdfdf', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'], dtype = 'object')

answered May 23 '19 at 08:34

Toni Sredanović

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U13-Forward · Accepted Answer · 2019-05-23T08:39:12.133

1

Change it by using dtype parameter to a very big number (e.g. 100):

>>> a=np.array(['dfdfdfdf', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'],dtype='<U100')
>>> a[0] = "hello there my friend"
>>> a
array(['hello there my friend', 'gulf', 'egypt', 'hijazi a', 'gulf',
       'egypt'], 
      dtype='<U100')
>>>

Or use:

>>> a=np.array(['dfdfdfdf', 'gulf', 'egypt', 'hijazi a', 'gulf', 'egypt'],dtype='<U100')
>>> a.dtype = '<U100'
>>> a[0] = "hello there my friend"
>>> a
array(['hello there my friend', 'gulf', 'egypt', 'hijazi a', 'gulf',
       'egypt'], 
      dtype='<U100')
>>>

edited May 23 '19 at 08:39

answered May 23 '19 at 08:34

U13-Forward

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can I change the dtype of an array var that already defined? – John Sall May 23 '19 at 08:38
@JohnSall see the second part, i edited my answer – U13-Forward May 23 '19 at 08:39
1

I'm changing " – John Sall May 23 '19 at 08:42

Array won't assign more than 8 characters in python

3 Answers3