打印新列表时，由于未定义新列表而出现错误

Question

def one(mylist):
    newlist=[]
    if len(mylist)>0:
        newlist.append(mylist[0])
    if len(mylist)>1:
        newlist.append(mylist[1])
    return newlist 

values = [35,40,50,38,20] 
print newlist
print one(newlist)
print newlist 

Its a small program that I am trying to run on python but getting error as newlist is not defined when printing new list. Why?

Answer 1

newlist array is defined inside the one function and its scope is limited to that function so it is inaccessible outside the function.

def one(mylist):
  newlist=[]
  if len(mylist)>0:
    newlist.append(mylist[0])
  if len(mylist)>1:
    newlist.append(mylist[1])
  return newlist 

values = [35,40,50,38,20] 
print one(values) #This will give the value of newlist returned from the 
#function

Or you can use:

newlist=one(values)
print newlist

Answer 2

Why your codes look so complex, it can be done in this way to avoid of judging the len(mylist) and initializing of newlist:

def one(mylist):
    newlist = mylist[0:2]
    return newlist


values = [35, 40, 50, 38, 20]

print(one(values))

The code above could handle the case when values is empty [ ] or has only one element;