CODEWITHSUNDEEP
pythontypes
python-coder
python-coder

Reputation: 35

When coding in Python, how do I achieve guarantees of correctness similar to those I get with Haskell's type system?

Using Haskell's type system I know that at some point in the program, a variable must contain say an Int of a list of strings. For code that compiles, the type checker offers certain guarantees that for instance I'm not trying to add an Int and a String.

Are there any tools to provide similar guarantees for Python code?

I know about and practice TDD.

Upvotes: 1

Views: 642

Answers (2)

snim2
snim2

Reputation: 4079

The quick answer is "not really". While tools like PyLint (which is very good BTW) will give you a lot of help and good advice on what constitutes good Python style, that isn't exactly what you're looking for and it certainly isn't a real substitute for things like HM type inference.

There are some interesting research projects in this area, notably Gradual Typing by Jeremy Siek and colleagues and some really interesting ideas like the blame calculus of Wadler and Findler.

Practically speaking, I think the best you can achieve is by using some sensibly chosen runtime methods. Use the inspect module to test the type of an object (but remember to be true to Python's duck typing and so on). Use assert statements liberally. Or (possible 'And') use something like Design by Contract using decorators. There are lots of ways to implement these idioms, but this is typically done on a per-project basis. You may want to think about whether and how such methods affect the performance and resource usage of your programs, if this is critical for you. There have, however, been some efforts to standardise techniques like DBC for Python, but these haven't (yet) been pushed into the cPython trunk. Here's hoping though :)

Upvotes: 3

Asterisk
Asterisk

Reputation: 3574

Python is dynamic and strongly typed programming language. What that means is that you can define a variable without explicitly stating its type, but when you first use that variable it becomes bound to a certain type.

For example,

x = 5 is an integer, and so now you cannot concatenate it with string, e.g. x+"hello"

Upvotes: 2

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