COMPUTE_NOT_PURE

What happened#

compute() changed one of the strategy's own attributes. Forge compares the strategy's attributes before and after compute() runs, and stops when one was added, removed or replaced. The message names the attribute.

Common causes#

• Setting an attribute on self inside compute(), such as self.count = 0.
• Replacing or deleting an attribute the strategy already had.

What to do#

Keep what compute() works out in local variables. compute() gets the data and the settings only, and keeps no state between runs.

Related#

• Strategy

Example#

strategy.py: compute() changed self.count. compute() gets the data and the settings only, and keeps no state between runs. [COMPUTE_NOT_PURE]

The wording of the message depends on your file, and the code does not.