python-3.x - StringIO 示例不起作用

Question

我尝试了解 numpy.getfromtxt 方法和 io.StringIO 的工作原理。在官方网站(https://docs.scipy.org/doc/numpy-1.13.0/reference/generated/numpy.genfromtxt.html#numpy.genfromtxt)我找到了一些例子。这是其中之一:

s = StringIO("1,1.3,abcde")
data = np.genfromtxt(s, dtype=[('myint','i8'),('myfloat','f8'),('mystring','S5')], delimiter=",")

但是当我在我的电脑上运行这段代码时，我得到:TypeError: must be str or None, not bytes

请告诉我如何解决它？

Answer 1

In [200]: np.__version__
Out[200]: '1.14.0'

这个例子对我有用:

In [201]: s = io.StringIO("1,1.3,abcde")
In [202]: np.genfromtxt(s, dtype=[('myint','i8'),('myfloat','f8'),
     ...: ... ('mystring','S5')], delimiter=",")
Out[202]: 
array((1, 1.3, b'abcde'),
      dtype=[('myint', '<i8'), ('myfloat', '<f8'), ('mystring', 'S5')])

它也适用于字节串:

In [204]: s = io.BytesIO(b"1,1.3,abcde")
In [205]: np.genfromtxt(s, dtype=[('myint','i8'),('myfloat','f8'),
     ...: ... ('mystring','S5')], delimiter=",")
Out[205]: 
array((1, 1.3, b'abcde'),
      dtype=[('myint', '<i8'), ('myfloat', '<f8'), ('mystring', 'S5')])

genfromtxt 可以处理任何输入行的东西，所以我通常直接使用字节串列表(测试问题时):

In [206]: s = [b"1,1.3,abcde"]
In [207]: np.genfromtxt(s, dtype=[('myint','i8'),('myfloat','f8'),
     ...: ... ('mystring','S5')], delimiter=",")
Out[207]: 
array((1, 1.3, b'abcde'),
      dtype=[('myint', '<i8'), ('myfloat', '<f8'), ('mystring', 'S5')])

或者多行

In [208]: s = b"""1,1.3,abcde
     ...: 4,1.3,two""".splitlines()
In [209]: s
Out[209]: [b'1,1.3,abcde', b'4,1.3,two']
In [210]: np.genfromtxt(s, dtype=[('myint','i8'),('myfloat','f8'),
     ...: ... ('mystring','S5')], delimiter=",")
Out[210]: 
array([(1, 1.3, b'abcde'), (4, 1.3, b'two')],
      dtype=[('myint', '<i8'), ('myfloat', '<f8'), ('mystring', 'S5')])

---

过去是dtype=None，genfromtxt创建了S个字符串。

NumPy dtype issues in genfromtxt(), reads string in as bytestring

在 1.14 中，我们可以控制默认的字符串数据类型:

In [219]: s = io.StringIO("1,1.3,abcde")
In [220]: np.genfromtxt(s, dtype=None, delimiter=",")
/usr/local/bin/ipython3:1: VisibleDeprecationWarning: Reading unicode strings without specifying the encoding argument is deprecated. Set the encoding, use None for the system default.
  #!/usr/bin/python3
Out[220]: 
array((1, 1.3, b'abcde'),
      dtype=[('f0', '<i4'), ('f1', '<f8'), ('f2', 'S5')])
In [221]: s = io.StringIO("1,1.3,abcde")
In [222]: np.genfromtxt(s, dtype=None, delimiter=",",encoding=None)
Out[222]: 
array((1, 1.3, 'abcde'),
      dtype=[('f0', '<i4'), ('f1', '<f8'), ('f2', '<U5')])

https://docs.scipy.org/doc/numpy/release.html#encoding-argument-for-text-io-functions

现在我可以使用 Py3 字符串生成示例，而不会产生所有那些难看的 b'string' 结果(但要记住并不是每个人都升级到 1.14):

In [223]: s = """1,1.3,abcde
     ...: 4,1.3,two""".splitlines()
In [224]: np.genfromtxt(s, dtype=None, delimiter=",",encoding=None)
Out[224]: 
array([(1, 1.3, 'abcde'), (4, 1.3, 'two')],
      dtype=[('f0', '<i4'), ('f1', '<f8'), ('f2', '<U5')])