~/tmp/rexp λ cat x.py
from mystery import a, b as b, c as d
~/tmp/rexp λ cat y.py
from x import a
from x import b
from x import c
from x import d
~/tmp/rexp λ mypy --no-implicit-reexport .
x.py:1: error: Cannot find implementation or library stub for module named 'mystery'
x.py:1: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
y.py:3: error: Module 'x' has no attribute 'c'
Found 2 errors in 2 files (checked 2 source files)

~/tmp/rexp λ mypy --no-implicit-reexport . 
x.py:1: error: Cannot find implementation or library stub for module named 'mystery'
x.py:1: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
y.py:1: error: Module 'x' does not explicitly export attribute 'a'; implicit reexport disabled
y.py:3: error: Module 'x' has no attribute 'c'
y.py:4: error: Module 'x' does not explicitly export attribute 'd'; implicit reexport disabled
Found 4 errors in 2 files (checked 2 source files)