73 – Slicing generators for debugging

When debugging with generators, you may want to use itertools.islice. This allows you to easily take a look at the first few elements of the generator.

You can wrap the call to islice in print(list(...)) to print the elements, or you can loop over the slice and add a breakpoint immediately before.

Here is an example using print(list(islice(..., n))) to print the first n elements immediately:

from itertools import islice

gen = mysterious_generator()

print(list(islice(gen, 3)))  # [0, 1, 4]

Remember that if you use islice again, you’ll be slicing from the remainder of the generator:

print(list(islice(gen, 3)))
# [9, 16, 25]
print(list(islice(gen, 3)))
# [36, 49, 64]