May I know why the following code does not print out [1,2,3,1,2,3]. Instead, it throws an exception. Could you show me how to make it work.
x = [1,2,3]
print apply(lambda x: x * 2, (x))
if I try the following, it works:
test1 = lambda x: x * 2
print test1(x)
apply will take its second argument (which should be a tuple/list) and passes each element of this tuple as positional argument to the object you passed to apply as first argument.
That means if x = [1,2,3] and you call
apply(lambda x: x * 2, (x))
apply will call the lambda function with the arguments 1, 2, and 3, which will fail, since the lambda function only takes a single argument.
To have it work, you should but x into a tuple or a list:
print apply(lambda x: x * 2, [x])
or
# note the extra ','. (x,) is a tuple; (x) is not.
# this is probably the source of your confusion.
print apply(lambda x: x * 2, (x,))
This works
x = [1,2,3]
print apply(lambda x: x * 2, [x])
However, it's probably worth noticing that apply is deprecated ever since Python 2.3
http://docs.python.org/2/library/functions.html#apply
Deprecated since version 2.3: Use function(*args, **keywords) instead of apply(function, args, keywords). (see Unpacking Argument Lists)
Maybe I do not understand your question, but if all you need is to "multiply" list, then simply multiply it:
xx = [1,2,3]
print(xx * 2)