On Thu, Jun 6, 2013 at 8:48 PM, Maccarthy, Jonathan K <jkmacc@lanl.gov> wrote:
Hi everyone,
I've looked in the mailing list archives and with the googles, but haven't yet found any hints with this question...
I have a float field in a NumPy record that looks like it's being substituted as a string in the Python "{:f}".format() mini-language, thus throwing an error:
In [1]: tmp = np.rec.array([('XYZZ', 2001123, -23.82396)], dtype=np.dtype([('sta', '|S6'), ('ondate', '<i8'), ('lat', '<f4')]))[0]
In [2]: type(tmp) Out[3]: numpy.core.records.record
In [3]: tmp Out[3]: ('XYZZ', 2001123, -23.823917388916016)
In [4]: tmp.sta, tmp.ondate, tmp.lat Out[4]: ('XYZZ', 2001123, -23.823917)
# strings and integers work In [5]: '{0.sta:6.6s} {0.ondate:8d}'.format(tmp) Out[5]: 'XYZZ 2001123'
# "lat" is a float, but it seems to be coerced to a string first, and failing In [6]: '{0.sta:6.6s} {0.ondate:8d} {0.lat:11.6f}'.format(tmp) --------------------------------------------------------------------------- ValueError Traceback (most recent call last) /Users/jkmacc/<ipython-input-312-bff8066cfde8> in <module>() ----> 1 '{0.sta:6.6s} {0.ondate:8d} {0.lat:>11.6f}'.format(tmp)
ValueError: Unknown format code 'f' for object of type 'str'
# string formatting for doesn't fail In [7]: '{0.sta:6.6s} {0.ondate:8d} {0.lat:>11.6s}'.format(tmp) Out[7]: 'XYZZ 2001123 -23.82'
This also fails:
In [7]: "{:f}".format(np.array(3.2, dtype='f4')) --------------------------------------------------------------------------- ValueError Traceback (most recent call last) /Users/jkmacc/<ipython-input-314-33119128e3e6> in <module>() ----> 1 "{:f}".format(np.array(3.2, dtype='f4'))
ValueError: Unknown format code 'f' for object of type 'str'
Does anyone understand what's happening?
numpy.ndarray does not implement the __format__() method. Thus, str.format() method falls back to object.__format__(). This is the exception that object.__format__() raises. Why it says "object of type 'str'" is not clear to me. Similarly, numpy.float32 does not implement the __format__() method. The string scalar type and the native integer scalar type (I assume you are on a 64-bit platform, so Python ints are 64-bit to match your 'i8' field) inherit from the corresponding native Python types, so they inherit their __format__() methods. -- Robert Kern