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up vote 3 down vote favorite

The code should speak for itself:

$ python
Python 3.3.0 (default, Dec 22 2012, 21:02:07) 
[GCC 4.7.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> '{}'.format(np.bytes_(b'Hello'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: maximum recursion depth exceeded while calling a Python object
>>> np.version.version
'1.7.0'

Both str and repr return "b'Hello'" on np.bytes_(b'Hello'), and I can print(np.bytes_(b'Hello')) just fine, but in a format string it falls into a recursion loop.

Am I being stupid or is it indeed what it appears to be, i.e. a problem in numpy? Even if it is, I don't quite understand what is happening. Can someone please explain?

I haven't reproduced it with Python 2.

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1 Answer 1

up vote 2 down vote accepted

The behaviour of {} is to call np.bytes_(b'Hello').__format__(). It seems there is a bug where __format__ is calling itself. See this related ticket

Here is a workaround.

Python 3.2.3 (default, Oct 19 2012, 19:53:57) 
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> '{}'.format(np.bytes_(b'Hello'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: maximum recursion depth exceeded while calling a Python object
>>> '{!s}'.format(np.bytes_(b'Hello'))
"b'Hello'"
>>> '{!r}'.format(np.bytes_(b'Hello'))
"b'Hello'"
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