Tips for restricted source in Python
Avoid &quot;normal&quot; letters
Identifiers are normalized by the Python 3 parser. This implies that cursive (Unicode) letters such as  are interpreted as their ASCII-compliant equivalents abcDEF. So the following code works (as was exploited here):
=123
()

Python versions in which this behaviour is confirmed:

Works: 3.4, 3.5, 3.6, 3.7, 3.8
Doesn't work: 2.7

Example source restriction:

Use no characters abc···xyz, ABC···XYZ.