How do I multiply each element in a list by a number?

You can just use a list comprehension:

my_list = [1, 2, 3, 4, 5]
my_new_list = [i * 5 for i in my_list]

>>> print(my_new_list)
[5, 10, 15, 20, 25]

Note that a list comprehension is generally a more efficient way to do a for loop:

my_new_list = []
for i in my_list:
    my_new_list.append(i * 5)

>>> print(my_new_list)
[5, 10, 15, 20, 25]

As an alternative, here is a solution using the popular Pandas package:

import pandas as pd

s = pd.Series(my_list)

>>> s * 5
0     5
1    10
2    15
3    20
4    25
dtype: int64

Or, if you just want the list:

>>> (s * 5).tolist()
[5, 10, 15, 20, 25]

Finally, one could use map, although this is generally frowned upon.

my_new_list = map(lambda x: x * 5, my_list)

Using map, however, is generally less efficient. Per a comment from ShadowRanger on a deleted answer to this question:

The reason “no one” uses it is that, in general, it’s a performance
pessimization. The only time it’s worth considering map in CPython is
if you’re using a built-in function implemented in C as the mapping
function; otherwise, map is going to run equal to or slower than the
more Pythonic listcomp or genexpr (which are also more explicit about
whether they’re lazy generators or eager list creators; on Py3, your
code wouldn’t work without wrapping the map call in list). If you’re
using map with a lambda function, stop, you’re doing it wrong.

And another one of his comments posted to this reply:

Please don’t teach people to use map with lambda; the instant you
need a lambda, you’d have been better off with a list comprehension
or generator expression. If you’re clever, you can make map work
without lambdas a lot, e.g. in this case, map((5).__mul__, my_list), although in this particular case, thanks to some
optimizations in the byte code interpreter for simple int math, [x * 5 for x in my_list] is faster, as well as being more Pythonic and simpler.