Python

Python 3: TypeError: unsupported format string passed to numpy.ndarray.__format__

This post explains how to work around a change in how Python string formatting works for numpy arrays between Python 2 and Python 3.

I’ve been going through Kevin Markham‘s scikit-learn Jupyter notebooks and ran into a problem on the Cross Validation one, which was throwing this error when attempting to print the KFold example:

Iteration                   Training set observations                   Testing set observations
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-28-007cbab507e3> in <module>()
      6 print('{} {:^61} {}'.format('Iteration', 'Training set observations', 'Testing set observations'))
      7 for iteration, data in enumerate(kf, start=1):
----> 8     print('{0:^9} {1} {2:^25}'.format(iteration, data[0], data[1]))
 
TypeError: unsupported format string passed to numpy.ndarray.__format__

We can reproduce this easily:

>>> import numpy as np
>>> "{:9}".format(np.array([1,2,3]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported format string passed to numpy.ndarray.__format__

What about if we use Python 2?

>>> "{:9}".format(np.array([1,2,3]))
'[1 2 3]  '

Hmmm, must be a change between the Python versions.

We can work around it by coercing our numpy array to a string:

>>> "{:9}".format(str(np.array([1,2,3])))
'[1 2 3]  '
Published on Web Code Geeks with permission by Mark Needham, partner at our WCG program. See the original article here: Python 3: TypeError: unsupported format string passed to numpy.ndarray.__format__

Opinions expressed by Web Code Geeks contributors are their own.

Do you want to know how to develop your skillset to become a Web Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. Building web apps with Node.js

2. HTML5 Programming Cookbook

3. CSS Programming Cookbook

4. AngularJS Programming Cookbook

5. jQuery Programming Cookbook

6. Bootstrap Programming Cookbook

 

and many more ....

 

I have read and agree to the terms & conditions

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments
Back to top button