If you absolutely want to use "in" instead of "==", then this is how:

string_A  =  "any"
string_B = "any string"

len(string_A) > 0 and string_A in string_B == True 

string_A = ""

len(string_A) > 0 and string_A in string_B == False

But.... if string_A is None then a Type Error is raised. But this also happens with a regular comparison with "==". So I leave it at that.

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