# BAD_CONSTRAINT

A constraint is not a function of the settings that returns True or False.

## What happened

A constraint is a function of the settings that returns True or False. It was not a function of one argument, `constraints` was not a list, or the function raised an error when it was tried on the defaults.

## What to do

Write each constraint as a function of one argument, for example `lambda p: p.fast < p.slow`, and keep them in a list.

## Example

```text
strategy.py, line 16: constraint 1 must be a function of one argument, like lambda p: p.fast < p.slow [BAD_CONSTRAINT]
```

The wording of the message depends on your file, and the code does not. An error stops the file from loading.