如何创建一个任意长度的字符串数组？

我是 Python 的新手，但是给定的字符串似乎可以(有效地)任意长度。也就是说，你可以取一个 string str并不断地加到它上面: str += "some stuff..."。有没有一种方法可以创建这样的字符串数组？

当我尝试这样做时，每个元素只存储一个字符

strArr = numpy.empty(10, dtype='string')
for i in range(0,10)
strArr[i] = "test"

另一方面，我知道我可以初始化一个特定长度的字符串数组，即。

strArr = numpy.empty(10, dtype='s256')

它可以存储多达256个字符的10个字符串。

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You could use the object data type:

>>> import numpy
>>> s = numpy.array(['a', 'b', 'dude'], dtype='object')
>>> s[0] += 'bcdef'
>>> s
array([abcdef, b, dude], dtype=object)
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最佳答案

You can do so by creating an array of dtype=object. If you try to assign a long string to a normal numpy array, it truncates the string:

>>> a = numpy.array(['apples', 'foobar', 'cowboy'])
>>> a[2] = 'bananas'
>>> a
array(['apples', 'foobar', 'banana'],
dtype='|S6')

But when you use dtype=object, you get an array of python object references. So you can have all the behaviors of python strings:

>>> a = numpy.array(['apples', 'foobar', 'cowboy'], dtype=object)
>>> a
array([apples, foobar, cowboy], dtype=object)
>>> a[2] = 'bananas'
>>> a
array([apples, foobar, bananas], dtype=object)

Indeed, because it's an array of objects, you can assign any kind of python object to the array:

>>> a[2] = {1:2, 3:4}
>>> a
array([apples, foobar, {1: 2, 3: 4}], dtype=object)

However, this undoes a lot of the benefits of using numpy, which is so fast because it works on large contiguous blocks of raw memory. Working with python objects adds a lot of overhead. A simple example:

>>> a = numpy.array(['abba' for _ in range(10000)])
>>> b = numpy.array(['abba' for _ in range(10000)], dtype=object)
>>> %timeit a.copy()
100000 loops, best of 3: 2.51 us per loop
>>> %timeit b.copy()
10000 loops, best of 3: 48.4 us per loop

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