The concat operator concatenates several observables. Each observable is concatenated to the previous one as soon as the previous observable completes. The following figure shows the marble diagram of this operator:

This operator can be used both as a class method and a static method. Its prototypes are the following ones:

Observable.concat(self, *args)
Observable.concat(cls, *args)

Here, args is either several observables to concatenate, or a list of observables.

Here is an example of the concat operator:

numbers1 = Observable.from_([1, 2, 3, 4])
numbers2 = Observable.from_([11, 12])

numbers1.concat(numbers2).subscribe(
    on_next = lambda i: print("on_next {}".format(i)),
    on_error = lambda e: print("on_error: {}".format(e)),
    on_completed = lambda: print("on_completed")
)

This example gives the following results:

on_next 1
on_next 2
on_next 3
on_next 4
on_next 11
on_next 12
on_completed