0

I am looking at some python code to control a camera and having some trouble understanding it due to being new at python. I see that the src parameter is set to 0. Does this mean that if a src is not given 0 will be used otherwise the given src will be used?

class WebcamVideoStream:

    def __init__(self, src=0):
        # initialize the video camera stream and read the first frame
        # from the stream
        self.stream = cv2.VideoCapture(src)

so if I do something like this 

vs = WebcamVideoStream(3)

then the src will be 3? and if I do this 

vs = WebcamVideoStream()

then src will be 0?

martineau
  • 119,623
  • 25
  • 170
  • 301
Lightsout
  • 3,454
  • 2
  • 36
  • 65
  • 2
    Yes indeed, that's the concept behind a default parameter. You can also name the parameter **explicitly**, like `WebcamVideoStream(src=14)` – Willem Van Onsem Feb 01 '17 at 23:22
  • 1
    https://docs.python.org/3/tutorial/controlflow.html#keyword-arguments – OneCricketeer Feb 01 '17 at 23:30
  • 1
    @cricket_007: Nah, you want the section on [default argument values](https://docs.python.org/3/tutorial/controlflow.html#default-argument-values). Keyword arguments are syntactically similar but not very related. – user2357112 Feb 01 '17 at 23:33
  • That type of construct in a function definition is called a "keyword argument" and always include a default value if it's omitted when the function is actually called. – martineau Feb 01 '17 at 23:33
  • @user2357112 Right. I missed that OP didn't mention calling with `Stream(src=)` – OneCricketeer Feb 01 '17 at 23:38

1 Answers1

0

Quick answer is - yes.

If you run:

vs = WebcamVideoStream(3)

src equals to 3

if you run:

vs = WebcamVideoStream()

src equals to 0(default value).

As an additional Python's feature, Python supports *args and **kwargs for cases when you're not sure how much and which arguments will be used in your method(it's very general explanation, but I hope it's clear).

Some example of using **kwargs I've posted here: http://codepad.org/E7m3PnVr

P.S.

1) use *args when you're not sure how many arguments might be passed to your function, i.e. it allows you pass an arbitrary number of arguments to your function.

2) **kwargs allows you to handle named arguments that you have not defined in advance

pivanchy
  • 723
  • 3
  • 15