Is Python type safe?

Question

According to Wikipedia

Computer scientists consider a language \"type-safe\" if it does not allow operations or conversions that violate the rules of the

Answer 1

in general, large scale / complex systems need type checking, first at compile type (static) and run time (dynamic). this is not academia, but rather a simple, common sense rule of thumb like "compiler is your friend". beyond runtime performance implication, there are other major implications, as following:

the 3 axis of scalability are:

1. build time (ability to design and manufacture safe systems in time and budget)
2. runtime (obvious)
3. maintain time (ability to maintain (fix bugs) and extend existing systems in a safe manner, generally by refactoring)

the only way to do safe refactoring is to have everything fully tested (use test driven development or at least unit testing and at least decent coverage testing as well, this is not qa, this is development/r&d). what is not covered, will break and systems like that are rather garbage than engineering artifacts.

now let's say that we have a simple function, sum, returning the sum of two numbers. one can imagine doing unit testing on this function, based on the fact that both parameters and returned type are known. we are not talking about function templates, which boil down to the trivial example. please write a simple unit test on the same function called sum where both parameters and return type can literally be of any kind, they can be integers, floats, strings and/or any other kind of user defined types having the plus operator overloaded/implemented. how do you write such a simple test case?!? how complex does the test case need to be in order to cover every possible scenario?

complexity means cost. without proper unit testing and test coverage, there no safe way to do any refactory, so the product is maintenance garbage, in not immediately visible, clearly in long term, because performing any refactoring in blind would be like driving a car without a driver license, drunk like a skunk and of course, without insurance.

go figure! :-)

Answer 2

We just had a big error in a piece of code. The error was because we had this:

   if sys.errno:
        my_favorite_files.append(sys.errno)

instead of this:

    if args.errno:
        my_favorite_files.append(sys.errno)

The aggressive casting anything to Boolean because it makes if statements easier is something that I would not expect to find in a language that is type-safe.