<p>Thanks for reporting this. From looking around, it looks like this was the consequence of a bug-fix in NumPy 1.16:</p>
<pre><code>Arrays based off readonly buffers cannot be set writeable
-------------------------------------------------------------
We now disallow setting the writeable flag True on arrays created
from fromstring(readonly-buffer).
</code></pre>
<p>PR in Numpy here: <a class="issue-link js-issue-link" data-error-text="Failed to load issue title" data-id="350543079" data-permission-text="Issue title is private" data-url="https://github.com/numpy/numpy/issues/11739" data-hovercard-type="pull_request" data-hovercard-url="/numpy/numpy/pull/11739/hovercard" href="https://github.com/numpy/numpy/pull/11739">numpy/numpy#11739</a></p>
<p>I am not familiar with the code in sequence.py but maybe <a class="user-mention" data-hovercard-type="user" data-hovercard-url="/hovercards?user_id=3976804" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/ebolyen">@ebolyen</a> can have a look? From some tinkering in the console, it looks like copying the data into a byte array and then passing that to <code>np.frombuffer</code> should suffice. For example:</p>
<p>This is what we have in _sequence.py.</p>
<pre><code># this fails 👎
In [1]: import numpy as np
...: s = 'asdf'.encode('ascii')
...: x = np.frombuffer(s, dtype=np.uint8)
...:
In [2]: x.flags.writeable = True
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-2-95da424ff829> in <module>
----> 1 x.flags.writeable = True
ValueError: cannot set WRITEABLE flag to True of this array
</code></pre>
<p>This is as inspired from some comments in the NumPy PR:</p>
<pre><code># this works 👍
In [3]: q = bytearray(4)
In [4]: q[:] = 'asdf'.encode('ascii')
In [10]: x = np.frombuffer(q, dtype=np.uint8)
In [11]: x.flags.writeable = True
</code></pre>
<hr>
<p>This is the <a href="https://github.com/biocore/scikit-bio/blob/master/skbio/sequence/tests/test_grammared_sequence.py#L238">failing unit test</a>.</p>
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