Demonstrates how `ignore = ` overrides the default ignore list, implicitly re-enabling optional warnings in bugbear. Note the line "Overriding default value of". Change bugbear version to 16.12.2 to see the workaround in action (note the line "Optional warning B950").

repro.sh

#!/bin/bash -e

# Create the environment
rm -rf .v  # remove old stuff if present
python3 -m venv .v
source .v/bin/activate
cd .v
pip install flake8==3.2.1
pip install flake8-bugbear==16.12.1  # the newer version works around the issue

# Create the flake8 config
cat <<EOF >.flake8
[flake8]
# implicitly re-enables B950
ignore = E501
EOF

# Create the script to evaluate
cat <<EOF >script.py
class C:
    """Long long line. Long long line. Long long line. Long long line. Long long line. Long long line. Long long line."""
    __metaclass__ = object
EOF

# Run flake8 to show you high-level errors and log Implicit vs. Explicit
flake8 --config=.flake8 -vvvv -j0 script.py 2>flake8_verbose.log || echo "flake8 correctly raised issues."

cat flake8_verbose.log | grep -E '(flake8\.options\.manager|flake8\.options\.aggregator|flake8\.style_guide|flake8\.bugbear)'