unsupported format string passed to numpy.ndarray

Question

Let's say I have the array:

import numpy as np
x = np.array([1.2334, 2.3455, 3.456], dtype=np.float32)

and want to print:

print('{:.2f}%'.format(x))

It gives me:

unsupported format string passed to numpy.ndarray.__format__

Hmm..The np.set_printoptions(precision=2) worked..I was wondering though why the above code doesn't work. — George
– George, Commented Oct 15, 2018 at 20:23
or as a string ('{:.2f} %'*len(x)).format(*x) yields '1.23 %2.35 %3.46 %' repeats the format string by the size of x, then starred x unravels to format. — NaN
– NaN, Commented Oct 16, 2018 at 3:22
The .format mechanism depends on what's been defined in the object's __format__ method. numpy developers haven't put much effort into expanding this beyond the basics ('!s' and '!r'). Note that your format string doesn't work for lists either. — hpaulj
– hpaulj, Commented Oct 17, 2018 at 7:19

BENY · Accepted Answer · 2018-10-15 20:34:22Z

14

If you still want format

list(map('{:.2f}%'.format,x))
Out[189]: ['1.23%', '2.35%', '3.46%']

answered Oct 15, 2018 at 20:34

BENY

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1 Comment

print("x=" + str(list(map('{:.2f}%'.format,x)))) That is, if you want to use "print" and combine text with "+", you must use str().

Aadil Rashid · Accepted Answer · 2021-03-04 08:34:14Z

2

Try this:

x = np.array([1.2334, 2.3455, 3.456], dtype=np.float32)

x= list(map(lambda x :str(x) + '%',x.round(2)))
print(f'{x}')

It would print:

['1.23%', '2.35%', '3.46%']

answered Mar 4, 2021 at 7:28

Aadil Rashid

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