I can print nested lists line by line by using for loop and " ".join() mapping each int in the nested list to a str with map().
Example:
>>> ys = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
>>> for xs in ys:
... print(" ".join(map(str, xs)))
...
1 2 3
4 5 6
7 8 9 10
But I am trying to figure out how to do this again without for loops that can support arbitrary lengths of inner lists. Any suggestions?
Since the depth is known and fixed, you can nest 2 map statements in a one-liner, using lambda to avoid comprehension (which would involve a for loop)
ys = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
print("\n".join(map(lambda xs : " ".join(map(str, xs)),ys)))
no for loop, at least none visible.
From a performance point of view, map performs a loop but problably compiled, so it is faster. On the other hand, join needs to know the size of the input so a list is created out of the iterable anyway, and join + list comprehension is then faster (not in Python 2 where map returns a list). In a word: use timeit to determine the fastest variant with your context.
map vs for-loop or map vs comprehension are not as straight-forward. See stackoverflow.com/a/39046254/5014455 There is also the added complication that built-in functions generally are mapped faster using map, compared to an equivalent list comprehension, but user-defined functions show the opposite pattern (comprehensions map faster than map).timeit will be the only judge :)ys = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
print "\n".join( [" ".join(map(str,subList)) for subList in ys] )
Code Explained:
[" ".join(map(str,subList)) for subList in ys]
This created a list of string with each value of each list combined with a space.
["1 2 3", "4 5 6", "7 8 9 10"]
"\n".join() is pretty self explantory after that.
EDIT:
Updated to use lambda instead of for.
ys = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
print "\n".join( map(lambda x: " ".join(map(str,x)),ys) )
lambda instead of for. Not sure if this will be okay.As a recursive function for any length/depth of lists:
def recursive_print_list(param):
while len(param) > 0:
if isinstance(param[0], list):
recursive_print_list(param[0])
print("")
param = param[1:]
else:
print(param[0], '', end='')
param = param[1:]
Worth noting the other two answers won't work for depth > 2. This will. It also relies on print()s implicit conversion to string, and will therefore work on any mixed input so long as you can print(element) all elements.
Original Answer:
xs = ys[:] # copy the original list, as this method is destructive
while True:
try:
print " ".join(map(str, xs[0]))
xs = xs[1:]
except IndexError:
break
will work for arbitrary nested lists of ints.
You could use the same method to avoid the map call as well: Python 3:
xs = ys[:]
while True:
if len(xs) == 0:
break
subl = xs[0][:]
while True:
try:
print(subl[0], ' ', sep='', end='')
subl = subl[1:]
except IndexError:
print("")
break
xs = xs[1:]
Python 2.7:
xs = ys[:]
while True:
if len(xs) == 0:
break
subl = xs[0][:]
while True:
try:
print subl[0],
subl = subl[1:]
except IndexError:
print ""
break
xs = xs[1:]
