1. Keyword Arguments aka Named Parameters in Ruby (and Python)
Matthew Cummings
@matthewcummings516
April 2015

2. About Me
Currently Test Automation Engineer at Spiceworks, a heavy Ruby/Rails shop
“Full Stack” test engineer. . . I do and have done a little bit of everything.
Acronym soup - C, C++, Perl, Javascript, Java, bash, Python and now Ruby
I love Python. . .
And Ruby!

3. Python and Ruby
My “dream” programming language would be a hybrid of the two, all the good parts, no bad parts.
WITHOUT A GIL! Python also has a GIL.
I’m still in the phase of comparing the two a lot. . . “Python, Ruby does THIS much better.”
“Now Ruby, do you know how easy THIS is in Python?”

4. Won’t go into the gory details, but
Both languages support several different ways of passing parameters.
Ruby’s options/param hash <-> Python’s foobar(**kwargs) parameter
Ruby’s splat foobar(*args) <-> Python’s foobar(*args), Python has no formal name for this.
Regular old positional args are the same: Ruby foobar(a,b,c) <-> Python foobar(a,b,c)

5. Parameters vs. Arguments
This is a bit pedantic, but there is a difference.
def foobar(x,y) -> x and y are parameters
foobar(1,2) > 1 and 2 are arguments

6. However. . .
Everyone uses the terms parameter and argument interchangeably. :)

7. Python’s Keyword Arguments
Python has had keyword arguments forever:
def foobar(param1=”default value”):
print param1
> foobar()
default value
> foobar("non-default value")
non-default value

8. Why they’re cool Provide a default value.
Argument order does not matter
def foobar(param1="default value",param2="hooray"):
print param1 + param2
> foobar(param1="default value", param2=", hooray!")
default value, hooray!
> foobar(param2=", hooray!", param1="default value")

9. Ruby’s default arguments
Pre-2.0, Ruby only had default arguments, which look exactly like Python’s keyword parameters:
def foobar(param1=”default value”)
print param1
end
> foobar
default value

10. But. . .
Unlike Python’s keyword arguments, parameter order DOES matter with Ruby’s default arguments.
def foobar(x=1,y=2)
puts "x is #{x}, y is #{y}"
end
> foobar(y=4,x=3)
x is 4, y is 3
Not what we expected!

11. Enter Ruby 2.0, Keyword Arguments
Argument order doesn’t matter.
def foobar(x:1,y:2)
puts "x is #{x}, y is #{y}"
end
> foobar(y:4,x:3)
x is 3, y is 4
That’s more like it!

12. Required Keyword arguments
Python cannot do this:
def foobar(x:, y:)
puts "x is #{x}, y is #{y}"
end
> foobar
ArgumentError: missing keywords: x, y

13. So when/why use them?
More than anything, I use them because they provide more runtime context when I call a method with incorrect arguments.

14. Compare this: def rectangle_area(width:, length:) puts width * length
end
> rectangle_area(1)
ArgumentError: missing keywords: width, length

15. With this: def rectangle_area(width, length) puts width * length end
ArgumentError: wrong number of arguments (1 for 2)

16. That’s all for now Questions? Links: