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Use Pylint for Code Checking inside Neovim

··724 words·4 mins·
Table of Contents

Pylint is a popular static code checker which can effectively find the possible bugs in your source code. It is easy to install pylint with conda or pip:

conda install pylint
# pip install pylint

Pylint configuration
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The pylint configuration file is named .pylintrc which controls its behaviors. Pylint will try to read the configuration from default locations. The locations of the configuration file vary from system to system:

  • Linux/Mac: ~/.pylintrc
  • Windows: %userprofile%\.pylintrc (%userprofile% is a system variable. You can use echo %userprofile% to show its value.)

You can disable certain warnings and errors in the configuration file, which will apply globally for every Python source file you check.

Usage
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pylint warning “module has no member"
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For Python packages which are partly written in C/CPP, such as Numpy and PyTorch, pylint may not be able to find the relevant method for an object. You can set up in [TYPECHECK] section of .pylintrc to disable warning about unfound method for Numpy and PyTorch:

[TYPECHECK]

# List of members which are set dynamically and missed by pylint inference
# system, and so shouldn't trigger E1101 when accessed. Python regular
# expressions are accepted.
generated-members=numpy.*,torch.*

Disable warning for a certain line
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If you only want to disable a certain warning or error for a specific line. You can add #pylint: disable=some-message,another-message in the end of the line. For example:

sys.path.insert(0, '..')
import mymodule  #pylint: disable=import-error

You can also use the warning or error code instead of the actual message:

sys.path.insert(0, '..')
import mymodule  #pylint: disable=E0401

Disable warning for a certain file
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If you want to disable a certain warning or error for a particular file, you can add #pylint: disable=some-message at the top of the file.

Find the msg id of a certain message
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To disable a certain warning, we want to know its message id. On the command line, use the following command:

pylint --list-msgs |grep message

For example, to find the message id of unnecessary-comprehension, we can use:

pylint --list-msgs|grep unnecessary-comprehension

We may also find the message id from pylint doc.

Configure and use pylint with Neovim
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To use pylint inside Neovim, you need to install a linting plugin. Neomake is a good choice. The minimum configuration for Neomake is:

" when to activate neomake
call neomake#configure#automake('nrw', 50)

" which linter to enable for Python source file linting
let g:neomake_python_enabled_makers = ['pylint']

Neomake will automatically run pylint for currently edited file and show warning and error symbols in sign column. You can also use :lopen to open the location list window to see all the warnings and errors. To navigate the location list, use :lprevious and :lnext to go to the previous and next item on the list respectively.

How to ignore warnings in Neomake
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When we lint our Python code with Neomake (using Pylint), it is often the case that our code can not pass the checker 100%. A lot of warnings and errors may occur, e.g., no docstring for method, variable names not conforming to standard. For some warnings, we do not want them to occur. How to ignore these warnings?

For example, if we want to ignore invalid-name(corresponding code is C0103) and missing-docstring（ corresponding code C0111），we can use two methods.

Configure in the nvim config file
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The first way is to configure through Nvim configuration file. Add the following settings to your Nvim configuration:

let g:neomake_python_pylint_maker = {
  \ 'args': [
  \ '-d', 'C0103, C0111',
  \ '-f', 'text',
  \ '--msg-template="{path}:{line}:{column}:{C}: [{symbol}] {msg}"',
  \ '-r', 'n'
  \ ],
  \ 'errorformat':
  \ '%A%f:%l:%c:%t: %m,' .
  \ '%A%f:%l: %m,' .
  \ '%A%f:(%l): %m,' .
  \ '%-Z%p^%.%#,' .
  \ '%-G%.%#',
  \ }

let g:neomake_python_enabled_makers = ['flake8', 'pylint']

Find the code corresponding to a warning and paste it in the string after -d options. Separate different warning codes with ,.

Configure in .pylintrc
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The second way is to create a .pylintrc file and ignore certain warning in this file. First, we need to generate .pylintrc under the home directory:

pylint --disable=invalid-namae,missing-docstring --generate-rcfile > ~/.pylintrc

If you want to ignore new warnings, you just need to edit .pylintrc, find the part starting with disable= and add the new warnings to the long list of existing warnings. The format should conform to the existing format in the .pylintrc file.

References
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