"[float(n)-50 for n in range(100)]" - what does this do?

Question

I stumbled upon this one-liner:

[float(n)-50 for n in range(100)]

Could somebody tell me what it does? It's supposed to return a float value for a vector.

Best, Marius

Answer 1

That's a list comprehension that reads "create a list of 100 elements such that for each element at index n, set that element equal to n-50".

Answer 2

It's a list comprehension:

List comprehensions provide a concise way to create lists. Common applications are to make new lists where each element is the result of some operations applied to each member of another sequence or iterable, or to create a subsequence of those elements that satisfy a certain condition.

For example, assume we want to create a list of squares, like:

>>> squares = []
>>> for x in range(10):
...     squares.append(x**2)
...
>>> squares 
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

We can obtain the same result with:

squares = [x**2 for x in range(10)]

This is also equivalent to squares = map(lambda x: x**2, range(10)), but it’s more concise and readable.