NumPy:旧数据描述符和新数据描述符的大小不匹配

在阅读CSV文件时,我遇到了NumPy 1.10.2的以下问题.我无法弄清楚如何给出明确的数据类型genfromtxt.

下面是CSV, minimal.csv:

x,y
1,hello
2,hello
3,jello
4,jelly
5,belly

在这里,我尝试用genfromtxt阅读它:

import numpy
numpy.genfromtxt('minimal.csv', dtype=(int, str))

我也尝试过:

import numpy
numpy.genfromtxt('minimal.csv', names=True, dtype=(int, str))

无论如何,我得到错误:

Traceback (most recent call last):
  File "visualize_numpy.py", line 39, in 
    numpy.genfromtxt('minimal.csv', dtype=(int, str))
  File "/Users/xeli/workspace/myproj/env/lib/python3.5/site-packages/numpy/lib/npyio.py", line 1518, in genfromtxt
    replace_space=replace_space)
  File "/Users/xeli/workspace/myproj/env/lib/python3.5/site-packages/numpy/lib/_iotools.py", line 881, in easy_dtype
    ndtype = np.dtype(ndtype)
ValueError: mismatch in size of old and new data-descriptor

或者,我试过:

import numpy
numpy.genfromtxt('minimal.csv', dtype=[('x', int), ('y', str)])

哪个投掷:

Traceback (most recent call last):
  File "visualize_numpy.py", line 39, in 
    numpy.genfromtxt('minimal.csv', dtype=[('x', int), ('y', str)])
  File "/Users/xeli/workspace/myproj/env/lib/python3.5/site-packages/numpy/lib/npyio.py", line 1834, in genfromtxt
    rows = np.array(data, dtype=[('', _) for _ in dtype_flat])
ValueError: size of tuple must match number of fields.

我知道dtype=None让NumPy尝试猜测正确的类型并且通常效果很好.但是,文档提到它比显式类型慢得多.在我的情况下,计算效率是必需的,因此dtype=None不是一种选择.

我的方法或NumPy有什么特别的错误吗？