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I have a structured numpy array.

The numpy structure matches the type google.protobuf.Timestamp.

I need to extract the seconds int64 and the nanos int32 from each element of said structure and assign it to the real Timestamp structure.

Below I list a script that does just that in a convenient way for anyone to test (numpy and protobuf Python modules need to be installed).

How do I get rid/circumvent the TypeError listed at the end and have the values out of the numpy structure in the Timestamp variable?

import numpy as np
from google.protobuf import timestamp_pb2

# numpy structure that mimics google.protobuf.Timestamp
Timestamp_t = np.dtype([('seconds', np.int64), ('nanos', np.int32)])

# populate numpy array with above structure
x_values_size = 3
x_values = np.empty((x_values_size,), dtype=Timestamp_t)
x_values['seconds'] = np.linspace(0, 100, num=x_values_size, dtype=np.int64)
x_values['nanos']   = np.linspace(0, 10, num=x_values_size, dtype=np.int32)

# copy data from numpy structured array to a descriptor-created Timestamp
for elem in np.nditer(x_values) :
    # destination protobuf structure (actually, part of some sequence)
    # try 1: this will actually change the type of 'ts'
    ts1 = timestamp_pb2.Timestamp()
    print(type(ts1)) # Timestamp as expected
    ts1 = elem
    print(ts1) # now a numpy.ndarray
    print(type(ts1))
    print(ts1.dtype)

    # try 2: assign member by member
    ts2 = timestamp_pb2.Timestamp()
    # fails with:
    # TypeError: array(0, dtype=int64) has type <class 'numpy.ndarray'>, but expected one of: (<class 'int'>,)
    ts2.seconds = elem['seconds']
    ts2.nanos = elem['nanos']
    print("-----")

Disclaimer: hardcore newbie when it comes to python and numpy arrays.

4

1 回答 1

1

所以

In [112]: x_values
Out[112]: 
array([(  0,  0), ( 50,  5), (100, 10)], 
      dtype=[('seconds', '<i8'), ('nanos', '<i4')])

nditer除非您需要特殊行为，否则我通常不建议使用。数组上的简单迭代（如果是 2d 则为行）通常是您所需要的。但是为了更好地理解发生了什么，让我们比较一下迭代方法：

In [114]: for elem in np.nditer(x_values):
     ...:     print(elem, elem.dtype)
     ...:     print(type(elem))   
(0, 0) [('seconds', '<i8'), ('nanos', '<i4')]
<class 'numpy.ndarray'>
(50, 5) [('seconds', '<i8'), ('nanos', '<i4')]
<class 'numpy.ndarray'>
(100, 10) [('seconds', '<i8'), ('nanos', '<i4')]
<class 'numpy.ndarray'>

In [115]: for elem in x_values:
     ...:     print(elem, elem.dtype)
     ...:     print(type(elem))
(0, 0) [('seconds', '<i8'), ('nanos', '<i4')]
<class 'numpy.void'>
(50, 5) [('seconds', '<i8'), ('nanos', '<i4')]
<class 'numpy.void'>
(100, 10) [('seconds', '<i8'), ('nanos', '<i4')]
<class 'numpy.void'>

相同，只是type不同，np.ndarrayv. np.void. nditer修改变量更容易。

做同样的事情，但只看一个字段：

In [119]: for elem in np.nditer(x_values):
     ...:     print(elem['seconds'], type(elem['seconds']))   
0 <class 'numpy.ndarray'>
50 <class 'numpy.ndarray'>
100 <class 'numpy.ndarray'>

In [120]: for elem in x_values:
     ...:     print(elem['seconds'], type(elem['seconds']))
0 <class 'numpy.int64'>
50 <class 'numpy.int64'>
100 <class 'numpy.int64'>

我没有protobuf代码，但我怀疑

ts2.seconds = elem['seconds']

第二次迭代会更好地工作，即产生np.int64值的迭代。或添加elem['seconds'].item().

于 2017-03-24T17:46:04.300 回答