I'm using a PYNQ board and i following some tutorials. In one of them they are using a for loop, but i dont understand well the syntax:
leds = [base.leds[index]) for index in range(MAX_LEDS)]
I mean, Why is one parenthesis? is a special syntax?
-
1Does this answer your question? What does "list comprehension" mean? How does it work and how can I use it?mkrieger1– mkrieger12020-04-18 19:45:13 +00:00Commented Apr 18, 2020 at 19:45
Add a comment
|
1 Answer
This is called a list comprehension.
List comprehensions are a special kind of expression in Python. List comprehensions return, well, a list. They are mainly meant to replace simple list-building code which would otherwise require a traditional for loop.
For example, the following loop:
leds = []
for index in range(MAX_LEDS):
leds.append(base.leds[index])
Can be rewritten as the list comprehension you have shown:
leds = [base.leds[index] for index in range(MAX_LEDS)]
List comprehensions also allow filtering on the items. So for example, the above loop can be further expanded to:
leds = []
for index in range(MAX_LEDS):
if 'green' in base.lends[index]:
leds.append(base.leds[index])
and can be converted to the following list comprehension:
leds = [base.leds[index] for index in range(MAX_LEDS) if 'green' in base.leds[index]]
Please read about the exact syntax online.
