创建列表时语法无效

Question

So i am attempting to create 3 different lists one of 1k, one of 10k, and one of 100k items long populated with random numbers from 1 to 10million but i cant seem to figure out why it keeps saying its invalid syntax. So far i have:

edit: okay it seems to have fixed the invalid syntax problem with some tweaking but still gives me:

Traceback (most recent call last):
  File "C:/Python32/funtime.py", line 16, in <module>
    print (list[1])
TypeError: 'type' object is not subscriptable

this is exactly what i have typed in:

import random

def createlist(a):

    blist =[]
    count=0
    while count <= a:

        blist.append(random.randint(1,10000000))
        count= count+1
    return blist;


list1= createlist(10000);

print (list[1])

Answer 1

Traceback (most recent call last):
  File "C:/Python32/funtime.py", line 16, in <module>
    print (list[1])
TypeError: 'type' object is not subscriptable

Objects of type type are indeed not subscriptable. list is the name of the builtin list class, which is an instance of type . It doesn't make any sense to subscript it, so that's clearly not what you intended to do.

You meant print (list1[1]) . list1 is the name you bound to your list object created by createlist(10000) .

The trick to finding these sort of bugs is to look at the error message Python gave you. It's telling you exactly the problem line, and exactly why it's a problem. All that was missing was the realisation that list is not the name of the object you wanted to subscript.

Answer 2

The following works fine on my system.

import random

def createlist(a):

    blist =[]
    count= 0
    while count <= a:
        blist.append(random.randint(1,1000000))
        count=count+1
    return blist

list1= createlist(10000)

print list1[1]

http://ideone.com/SL2bL <-- try it here.

I'd probably do it like this

import random

def createlist(a):

    return [random.randint(1,1000000) for i in xrange(a)]


list1= createlist(10000)

print list1[1]

Or probably just skip the function..

list1 = [random.randint(1,1000000) for i in xrange(a)]
print list1[1]

Answer 3

A much shorter version would be:

>>> import random
>>> def create_list(length):
...     return [random.randint(1,1000000) for _ in range(length)]

This demonstrates a couple of things:

1. A much more compact way to loop x times (the for _ in range(length) idiom)
2. List comprehensions to create lists, instead of repeated calls to append .
3. The use of _ as a variable name when you need the variable, but not the actual data in it. This is a somewhat common convention that crops up most often in list comprehensions. It isn't a problem not to use it, but it crops up often enough that it pays to be aware of it.

Hat-tip to @mgilson for his comment on another answer that reminded me the _ convention.

Answer 4

使用列表理解（它的方式betta，让你看起来亲，哈哈）

[random.randint(1, 1000000) for i in range(10000)]

Answer 5

As some other answers have stated, you could easily use list comprehension for something like this (the so-called Pythonic way):

somelist = [random.randint(1, 1000000) for i in xrange(10000)]

List comprehension is fast in Python because it is executed by underlying C code. Moreover, using xrange is more memory-efficient.

Note: By convention, when the loop-control variable is not used in Python, it is named _ :

somelist = [random.randint(1, 1000000) for _ in xrange(10000)]

Answer 6

First, you don't put a paren by while unless you're evaluating complex expressions.

Next, you used a semicolon to return your blist . Not necessary.

Finally...why not use a for loop?

import random

def createlist(a): 
    blist =[]

    for x in xrange(a):
        blist.append(random.randint(1,1000000))

    return blist

list1= createlist(10000)

print list1[0]