Undefined name: 'vocab' in mxnet.py

[cclauss]

@astonzhang https://github.com/d2l-ai/d2l-en/blob/master/d2l/mxnet.py#L2222-L2223 on these lines vocab is an undefined name.

flake8 testing of https://github.com/d2l-ai/d2l-en on Python 3.8.3

$ flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics

./d2l/mxnet.py:2222:24: F821 undefined name 'vocab'
    premise = np.array(vocab[premise], ctx=d2l.try_gpu())
                       ^
./d2l/mxnet.py:2223:27: F821 undefined name 'vocab'
    hypothesis = np.array(vocab[hypothesis], ctx=d2l.try_gpu())
                          ^
2     F821 undefined name 'vocab'
2

https://flake8.pycqa.org/en/latest/user/error-codes.html

On the flake8 test selection, this PR does not focus on "style violations" (the majority of flake8 error codes that psf/black can autocorrect). Instead these tests are focus on runtime safety and correctness:

• F82 tests are almost always undefined names which are usually a sign of a typo, missing imports, or code that has not been ported to Python 3. These also would be compile-time errors in a compiled language but in Python a NameError is raised which will halt/crash the script on the user.
• E9 tests are about Python syntax errors usually raised because flake8 can not build an Abstract Syntax Tree (AST). Often these issues are a sign of unused code or code that has not been ported to Python 3. These would be compile-time errors in a compiled language but in a dynamic language like Python they result in the script halting/crashing on the user.
• F63 tests are usually about the confusion between identity and equality in Python. Use ==/!= to compare str, bytes, and int literals is the classic case. These are areas where a == b is True but a is b is False (or vice versa). Python >= 3.8 will raise SyntaxWarnings on these instances.
• F7 tests logic errors and syntax errors in type hints

[goldmermaid]

Hi thanks for raising the issue. I had a PR https://github.com/d2l-ai/d2l-en/pull/951.

[xiaotinghe]

PR #953

[astonzhang]

Thanks @goldmermaid and @xiaotinghe . It's fixed now.

[cclauss]

Fixed in #953