使用列表推导和input（）的麻烦

Question

Trying to write a list comprehension that can iterate through a string from input() and create a list with each character of the string having it's own index.

In essence, I want a function that does this:

x = ["00.00"[h] for h in range(len("00.00"))]
print(x)
> ['0', '0', '.', '0', '0']

When putting an actual string ("00.00") in there, python does exactly what I want it to do. But it refuses to take an input() the same way:

>>> x = [input()[h] for h in range(len(input()))]
> what

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
IndexError: string index out of range

The word "what" in there is what i inputted, but it does the same for basically everything else I've put in. I'm not sure what's so different about input() that changes how the indexes work. What is it?

Answer 1

You produced a rather long-winded spelling of list() . There is no need to use list comprehension here:

list(input())

What goes wrong for you is that the expression at the front of the list comprehension is evaluated for every single iteration ; so you call input() first to get a string, then for every character in that string you call input() again , but this time the input is not necessarily the same string.

If you ever do need a list comprehension over a string, just iterate over the string directly. The Python for loop is a for each construct , there is no need to generate an index; for example, to filter the input to produce a list of lowercase ASCII letters, there is no need to use range() :

[char for char in input() if 'a' <= char <= 'b']