A slightly faster interpose.

[groutr]

Special case the removal of the first element. Consumes the first element with a call to next() instead of using islice.

The downside is the function could be considered "less beautiful". Though, new implementation does make a certain logical sense. We construct the interposed sequence in one line, then throw away the first element and return the rest of it.

Timings:

# With Python 3.5.3 (conda-forge)
%timeit tuple(interpose('\n', range(1)))
1000000 loops, best of 3: 1.54 µs per loop
%timeit tuple(fast_interpose('\n', range(1)))
1000000 loops, best of 3: 1.33 µs per loop

%timeit tuple(interpose('\n', range(5)))
1000000 loops, best of 3: 1.88 µs per loop
%timeit tuple(fast_interpose('\n', range(5)))
1000000 loops, best of 3: 1.66 µs per loop

%timeit tuple(interpose('\n', range(1000000)))
10 loops, best of 3: 100 ms per loop
%timeit tuple(fast_interpose('\n', range(1000000)))
10 loops, best of 3: 94 ms per loop

[eriknw]

Looks good to me. Merging. Thanks, @groutr!

[groutr]

Thanks @eriknw