I am a new programmer learning python with Codeacademy and I am supposed to create a function double_list that returns the items in list n and multiplies each number by 2. Every time I run the code I get the error: ' double_list([0, 1]) returned [0, 1] instead of [0, 2]'
n = [3, 5, 7]
def double_list(x):
for i in range(0, len(x)):
x[i] = x[i] * 2
return x
print double_list(n)
Your function can only return once, so you need to back it out of the for loop. As written, your function currently will return x after the first iteration, so none of the remaining elements are modified.
def double_list(x):
for i in range(0, len(x)):
x[i] = x[i] * 2
return x
An alternative, by the way, is to use a simple list comprehension, this will not modify the original list and will create a new one that you can assign back to the original variable if you'd like
def double_list(x):
return [i*2 for i in x]
>>> n = [3, 5, 7]
>>> n = double_list(n)
>>> n
[6, 10, 14]
If you prefer to modify the actual list argument, you can use change the function to
def double_list(x):
for index, value in enumerate(x):
x[index] = 2 * value
>>> n = [3, 5, 7]
>>> double_list(n)
>>> n
[6, 10, 14]
return AT ALL (much how list.sort() returns None -- it's just an in-place mutation)
you can do it very easy with list comprehension.
n = [3, 5, 7]
def double_list(x):
return [y*2 for y in x]
print double_list(n)
'[6, 10, 14]'
This is an easy way to do it using map:
>>> n = [3, 5, 7]
>>> def double_list(x):
return x * 2
>>> map(double_list, n)
[6, 10, 14]
>>>
use map can simply it:
n = map(lambda x: 2*x, n)
n = [3, 5, 7]
def double_list(x):
for i in range(0, len(x)):
x[i] = x[i] * 2
return x
print double_list(n)
You just need to change n to x in the above line and you'll pass through this exercise
You can simply do this:
n = [3, 5, 7]
def double_list(x):
for i in range(0, len(x)):
x[i] = x[i] * 2
for j in range(1, len(x)):
x[j] = x[j] * 2
for k in range(2, len(x)):
x[k] = x[k] * 2
return x
# Don't forget to return your new list!
print double_list(n)
