Python - Initializing Multiple Lists/Line
PythonListInitializationPython Problem Overview
This is terribly ugly:
psData = []
nsData = []
msData = []
ckData = []
mAData = []
RData = []
pData = []
Is there a way to declare these variables on a single line?
Python Solutions
Solution 1 - Python
alist, blist, clist, dlist, elist = ([] for i in range(5))
The downside of above approach is, you need to count the number of names on the left of =
and have exactly the same number of empty lists (e.g. via the range
call, or more explicitly) on the right hand
side.
The main thing is, don't use something like
alist, blist, clist, dlist, elist = [[]] * 5
nor
alist = blist = clist = dlist = elist = []
which would make all names refer to the same empty list!
Solution 2 - Python
psData,nsData,msData,ckData,mAData,RData,pData = [],[],[],[],[],[],[]
Solution 3 - Python
Depending on your needs, you could consider using a defaultdict with a list factory. Something like:
my_lists = collections.defaultdict(list)
and then you can directly append to my_lists["psData"] and so on. This is the relevant doc page: http://docs.python.org/library/collections.html#collections.defaultdict
Solution 4 - Python
A bit more efficient approach:
alist, blist, clist, dlist, elist = ([] for _ in xrange(5))
[NOTE]:
-
xrange()
is more optimal thanrange()
in Python2. (https://stackoverflow.com/questions/94935/what-is-the-difference-between-range-and-xrange-functions-in-python-2-x">Ref</a>)</sup> -
The
i
variable was unusable so using_
is better. (https://stackoverflow.com/a/47599668/3702377">Ref</a>)</sup> -
xrange()
is no longer in Python3 —range()
is the same withxrange()
.
Solution 5 - Python
Bare in mind that, tidiness may come with consequences of performance. The range function call will slow down the init process slightly. Beware if you have some process that need to reinit the variable many time.
import time
def r_init():
st=time.time()
alist, blist, clist, dlist, elist = ([] for i in range(5))
et=time.time()
print("{:.15f}".format(et-st))
def p_init():
st=time.time()
alist=[];blist=[];clist=[];dlist=[];elist=[]
et=time.time()
print("{:.15f}".format(et-st))
for x in range(1,10):
r_init()
p_init()
print("\n")
Solution 6 - Python
You can use a class to initialize/store the data, it would take more lines, but could be easier to read, and more object oriented.
Like:
class Data:
def __init__(self):
self.var1=[]
<etc.>
def zeroize(self):
self.var1=[]
<etc.>
Then in main near the beginning:
data=Data()
Then in your loops or anywhere in main post declaration you can use the class.
data.var1.append(varN)
if(something):
data.zeroize()
Solution 7 - Python
Something along the lines of
alist, blist, clist, dlist, elist = ([],)*5
would appear to be the most elegant solution.