When two string literals abut each other the Python interpreter implicitly concatenates them into a single string. On occasion this can be useful, but is more commonly misleading or incorrect.

If the concatenation is deliberate, then use + to join the strings. This has no runtime overhead, and makes the intention clear.

In the first function below, unclear, implicit string concatenation is used twice; once deliberately and once by accident. In the second function, clarified, the first concatenation is made explicit and the second is removed.

Python language reference: String literal concatenation.