为什么列表在python中包含超过n个元素？

Question

I am novice in Python. I would like to enter 10 elements into the list. Below program appends 10 elements to each of the list. But below program prints 11 objects in list why? I got this program from http://www.learnpython.org/page/Basic%20Operators link. I wanted to know x = object() , what does it mean?

x = object()
y = object()
i = 0
# change this code
x_list = [x]
y_list = [y]
while(i < 10):
    x_list.append((10))
    y_list.append(11)
    i = i + 1
#x_list = [x]
#y_list = [y]
big_list = x_list + y_list

print "x_list contains %d objects" % len(x_list) # prints 11 objects, #Why?
print "y_list contains %d objects" % len(y_list) # prints 11 objects, #Why?
print "big_list contains %d objects" % len(big_list)
print x_list.count(10)
print y_list.count(11)
    print big_list.count(10)
# testing code
if x_list.count(x) == 10 and y_list.count(y) == 10:
    print "Almost there..."
if big_list.count(x) == 10 and big_list.count(y) == 10:
    print "Great!"

Answer 1

x_list = [x] => 1 object. while(i < 10): x_list.append((10)) => 10 objects (0 to 9) So 11 is perfectly normal. You should have set x_list = [] (empty list) not to have this 1st element.

Answer 2

The learnpython.org basic operators page provides some examples of using arithmetic operators in different contexts, including lists. Based on quickly reading the tutorial in that page, probably the answer that the page authors were after would be:

x_list = [x] * 10
y_list = [y] * 10
big_list = x_list + y_list

Which would create a list with 10 x:s in it.

You were using a loop to do that, which is much more flexible way. A more pythonic way to fill a list by using a loop would be eg to use list comprehensions:

x_list = [x for i in xrange(10)]

or use a for loop, then you don't have to keep track of the index yourself:

for i in xrange(10):
    x_list.append(x)

Answer 3

Below program appends 10 elements to each of the list. But below program prints 11 objects in list why?

Because the list had 1 element in it before you started appending. The list [x] contains 1 element, x . 1 + 10 = 11.

I wanted to know x = object(), what does it mean?

It means exactly what it says: "x shall be a name for the result of calling object ". object is a class, so calling it creates an instance. An object instance is exactly what it sounds like - just an object, with nothing interesting about it.

Answer 4

object() just generates a new instance of the class object . you first insert this element to x_list , then you add another 10 elements

Answer 5

x_list contains X plus 10 times 10 = 11...

y_list - the same.

when you type x_list = [x] it means the list is initialized as a list with only x in it.