1️⃣ single leading underscore ("_var"): indicates that the variable is meant for internal use. This is not enforced by the interpreter and is rather a hint to the programmer.
2️⃣ single trailing underscore ("var_"): it's used to avoid conflicts with Python reserved keywords ("class_", "def_", etc.)
3️⃣ double leading underscores ("__var"): Triggers name mangling when used in a class context and is enforced by the Python interpreter. What this means is that it should be used to avoid your method is being overridden by a subclass or accessed accidentally.
4️⃣ double leading and trailing underscores ("var"): used for special methods defined in the Python language (ex. init, len, call, etc.). They should be avoided to use for your own attributes.
5️⃣ single underscore (""): Generally used as a temporary or unused variable. (If you don't use the running index of a for-loop, you can replace it with "").