python中的错误：名称'...'未定义

Question

I am using a list to store some values.

Sample code:

for i in range(3):
  print i
  lst[i] = i+1
  print lst[i]

But i am getting an error like this:

lst[i] = i+1
NameError: name 'lst' is not defined

Is it required to initialize an array in python? What is wrong in my code?

Answer 1

Here's your code:

    for i in range(3):
        print i
        lst[i] = i+1
        print lst[i]

there are two things wrong with it

1- you havn't initialize your list, the computer doesn't know yet that you are working with a list (like you do in programs where u keep track of a counter variable like count = count + i because it must have a seed value to start with)
2- you cannot append elements to a list with the assignment operator, use the append function for that.

so here's the correct code:

    lst = []
    for i in range(3):
        print(i)
        lst.append(i+1)
    print(lst[i])

output : 0 1 2 3

Answer 2

You should initalise lst as list lst=[]

lst=[]
for i in range(3):
  print i
  lst.append(i+1)
  print lst[i]

Another way you can do it; the above 5 lines are equivalent to the following single-line list comprehension, except for the printing:

lst=[i+1 for i in range(3)]

Answer 3

Yes, you should

lst=[]
for i in range(3):
  print i
  lst.append(i+1)
  print lst[i]

Answer 4

lst = []
for i in range(3):
    print i
    lst.append(i+1)
    print lst[i]