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Error codes

Mypy can optionally display an error code such as [attr-defined] after each error message. Error codes serve two purposes:

  1. It's possible to silence specific error codes on a line using # type: ignore[code]. This way you won't accidentally ignore other, potentially more serious errors.
  2. The error code can be used to find documentation about the error. The next two topics (error-code-list and error-codes-optional) document the various error codes mypy can report.

Most error codes are shared between multiple related error messages. Error codes may change in future mypy releases.

Displaying error codes

Error codes are not displayed by default. Use --show-error-codes <mypy --show-error-codes> or config show_error_codes = True to display error codes. Error codes are shown inside square brackets:

$ mypy --show-error-codes prog.py
prog.py:1: error: "str" has no attribute "trim"  [attr-defined]

It's also possible to require error codes for type: ignore comments. See ignore-without-code<ignore-without-code> for more information.

Silencing errors based on error codes

You can use a special comment # type: ignore[code, ...] to only ignore errors with a specific error code (or codes) on a particular line. This can be used even if you have not configured mypy to show error codes. Currently it's only possible to disable arbitrary error codes on individual lines using this comment.

You can also use --disable-error-code <mypy --disable-error-code> to disable specific error codes globally.

This example shows how to ignore an error about an imported name mypy thinks is undefined:

# 'foo' is defined in 'foolib', even though mypy can't see the
# definition.
from foolib import foo  # type: ignore[attr-defined]

Enabling specific error codes

There are command-line flags and config file settings for enabling certain optional error codes, such as --disallow-untyped-defs <mypy --disallow-untyped-defs>, which enables the no-untyped-def error code.

You can use --enable-error-code <mypy --enable-error-code> to enable specific error codes that don't have a dedicated command-line flag or config file setting.