Please include a "how to fix it" example in the error message

[bbkane]

Note: if you are reporting a wrong signature of a function or a class in
the standard library, then the typeshed tracker is better suited
for this report: https://github.com/python/typeshed/issues

Please provide more information to help us understand the issue:

• Are you reporting a bug, or opening a feature request?

Feature request. A slightly more clear error message, which might be appreciated by folks newer to Python who aren't as familiar with the mini formatting language. If wanted, I'll contribute a pull request to fix this.

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

$ cat tmp.py
print("{}".format(b'abc'))

• What is the actual behavior/output?

$ mypy tmp.py
tmp.py:1: error: On Python 3 '{}'.format(b'abc') produces "b'abc'"; use !r if this is a desired behavior
Found 1 error in 1 file (checked 1 source file)

• What is the behavior/output you expect?

I'd love an example of what exactly to change. Something like:

$ mypy tmp.py
tmp.py:1: error: On Python 3 '{}'.format(b'abc') produces "b'abc'"; use !r if this is a desired behavior. Example: '{!r}'.format(b'abc'
Found 1 error in 1 file (checked 1 source file)

• What are the versions of mypy and Python you are using?

$ python3 --version
Python 3.7.6

$ mypy --version
mypy 0.770

Do you see the same issue after installing mypy from Git master?

The error source code is still the same in Git master

• What are the mypy flags you are using? (For example --strict-optional)

No flags

• If mypy crashed with a traceback, please paste
  the full traceback below.

(You can freely edit this text, please remove all the lines
you believe are unnecessary.)

[hauntsaninja]

I had a colleague get confused by this error message recently too. Linked PR should resolve :-)