Rule Definition
Trailing whitespace left in source code is generally inocuous. There is a single exception in Python: if the line continuation backslash marker is followed by an unintentional space and a newline, then it is not interpreted as a line continuation. Besides this syntactic issue, non-meaningful differences in files might get registered because of trailing whitespace addition or removal. It is thus recommended to avoid trailing whitespaces in code.

Remediation
Most editors can be configurated to automatically remove trailing whitespace from code.

PEP-8