How to know function return type and argument types?

Solution 1:

Well things have changed a little bit since 2011! Now there's type hints in Python 3.5 which you can use to annotate arguments and return the type of your function. For example this:

def greeting(name):
  return 'Hello, {}'.format(name)

can now be written as this:

def greeting(name: str) -> str:
  return 'Hello, {}'.format(name)

As you can now see types, there's some sort of optional static type checking which will help you and your type checker to investigate your code.

for more explanation I suggest to take a look at the blog post on type hints in PyCharm blog.

Solution 2:

This is how dynamic languages work. It is not always a good thing though, especially if the documentation is poor - anyone tried to use a poorly documented python framework? Sometimes you have to revert to reading the source.

Here are some strategies to avoid problems with duck typing:

create a language for your problem domain
this will help you to name stuff properly
use types to represent concepts in your domain language
name function parameters using the domain language vocabulary

Also, one of the most important points:

keep data as local as possible!

There should only be a few well-defined and documented types being passed around. Anything else should be obvious by looking at the code: Don't have weird parameter types coming from far away that you can't figure out by looking in the vicinity of the code...

Related, (and also related to docstrings), there is a technique in python called doctests. Use that to document how your methods are expected to be used - and have nice unit test coverage at the same time!

Solution 3:

I attended a coursera course, there was lesson in which, we were taught about design recipe.

Below docstring format I found preety useful.

def area(base, height):
    '''(number, number ) -> number    #**TypeContract**
    Return the area of a tring with dimensions base   #**Description**
    and height

    >>>area(10,5)          #**Example **
    25.0
    >>area(2.5,3)
    3.75
    '''
    return (base * height) /2

I think if docstrings are written in this way, it might help a lot to developers.

Link to video [Do watch the video] : https://www.youtube.com/watch?v=QAPg6Vb_LgI

Solution 4:

Actually there is no need as python is a dynamic language, BUT if you want to specify a return value then do this

def foo(a) -> int: #after arrow type the return type 
       return 1 + a

In the example above it will return int if you will give a string perimeter such as "hello" to it then it will throw this exception TypeError: unsupported operand type(s) for +: 'int' and 'str' because it has asked for a int value and we gave it a string value and lastly because we can't add int and string

and then for argument type do this

def foo(a: int) -> int:
      return a+ 1

after the colon (:)you can specify the argument type

How to know function return type and argument types?

Solution 1:

Solution 2:

Solution 3:

Solution 4:

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