use list for function arguments in python

Question

I cant get my head around how to do this. I have a nested list, which I want to use as function arguments.

The function.

pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, {commands} ])

I would like to loop through the list so the end result is like below.

NestedList = [[1,2,3,4,5,6,7,8],[2,0,2,0,2,0],[0,0,1,1,0,0]]

pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, 1,2,3,4,5,6,7,8 ])
pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, 2,0,2,0,2,0 ])
pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, 0,0,1,1,0,0 ])

If i try using this;

for i in NestedList:
  pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, i ])

I get this errror; TypeError: an integer or string of size 1 is required

This is because the function is expecting bytes and the loop above is placing in an actual list of bytes.. E.g. pi.bb_i2c_zip(SDA, [4, address, 2, 7,18,[1,2,3,4,5,6,7,8]])

in summary, how can I place; 1,2,3,4,5,6,7,8 into the function and not this [1,2,3,4,5,6,7,8]

pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, *i ])

Epsi95
– Epsi95

2021-07-08 14:55:44 +00:00
Commented Jul 8, 2021 at 14:55 — Epsi95
– Epsi95, Commented Jul 8, 2021 at 14:55

chepner · Accepted Answer · 2021-07-08 14:55:58Z

4

You have to unpack the list first.

for i in NestedList:
  pi.bb_i2c_zip(SDA, [4, address, 2, 7,18, *i ])

Otherwise, your list argument is just another nested list. The * unpacking is more efficient (though possibly less clear) than [4, address, 2, 7, 18] + i. Unpacking also works with any iterable i, whereas + requires conversion of i to a list (i.e., [...] + list(i)).

answered Jul 8, 2021 at 14:55

chepner

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2 Comments

flakes Over a year ago

"The * unpacking is more efficient (though possibly less clear)" Personally looks clear to me. I would probably just rename i to something more meaningful.

chepner Over a year ago

I very much like [..., *i], but I don't think it's obvious at first glance that prefixing a * will expand the iterable to its elements. It's certainly a good idiom once you adjust to it, though.

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