Why Does Flake8 Object to Boolean Comparisons in SQLAlchemy Filters, and How Can I Fix It?

Flake8's Objection to Boolean Comparison in Filter Clauses

Code linters often raise warnings to promote best practices in programming. One such warning is flake8's E712, which flags boolean comparisons using "==" in filter clauses. This article explores the issue and provides alternative ways to express boolean conditions in SQLAlchemy queries.

Flake8's Warning

As illustrated in the provided code snippet, flake8 warns against expressions like "TestCase.obsoleted == False" in filter clauses. According to flake8, these comparisons should be written as "if cond is False:" or "if not cond:".

SQLAlchemy's Treatment of Boolean Comparisons

However, the provided code works as intended despite the warning. This is because SQLAlchemy filters are an exception to the general rule. In this context, "==" is an acceptable way to compare boolean fields.

Alternatives for Boolean Conditions in Filter Clauses

While "==" is acceptable in SQLAlchemy filters, it is recommended to use alternative approaches that align with best practices. Two solutions are:

• Disable Flake8 Warning: By adding a "# noqa" comment to the problematic line, you can suppress the warning.
• Use SQLAlchemy's false() Function: SQLAlchemy provides a function called "false()" that returns the appropriate boolean value for the session's SQL dialect. You can use this function to create boolean conditions like:

from sqlalchemy.sql.expression import false

TestCase.obsoleted == false()

This approach not only addresses flake8's concerns but also ensures compatibility with different SQL dialects.

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