Python generates the error message you present in your question whenever you call the int() builtin function with a string argument that cannot be parsed as an integer; and, in fact, the error message shows you the precise string it was trying to parse as an integer: namely ‘0.25’.
How to fix the error? It depends on what you want to do.
If what you want is to parse and convert the string to a numeric value, this particular string clearly contains a numeric representation which is not an integer but a real. The way to “fix” the error in this case is to invoke the float() builtin function, which returns a floating point (real) value. If you really wanted an integer, despite having a real in the string, use int(float(your_value_here)). Note that this converts the string to a floating point value, which is then converted to an integer via truncation—that is, by discarding the fractional part. Applying these functions to ‘0.25’ will produce a result of 0. If, on the other hand, you wanted the floating point value, just use float().
Or, perhaps, you didn’t expect the ‘0.25’. In this case, find where that string comes from and fix the problem at the origin. Can’t help you there, though, as I don’t know your code and how that string got to the int() call.