将项目存储在 Python 的列表中

Question

I am new to python and would like to ask a simple question.

I am trying to get this program to loop and every time it loops, it should store a variable in a list.

Please help

This is my code so far:

import random
for x in range(1,100):
    q=random.randint(0,99)
    w=random.randint(0,99)
    e=q*w
    q=[]#This is the list
    print '%s * %s = %s'%(q,w,e)

Answer 1

You need to define the list outside of the loop, and append to it within the loop.

import random

# Define your list
l = []
for x in range(1,100):
    q=random.randint(0,99)
    w=random.randint(0,99)
    e=q*w
    # Append the result to your list
    l.append(e)
    print '%s * %s = %s'%(q,w,e)

print 'The list becomes: %s' % l

Answer 2

Let's go through your code line-for-line

import random

for x in range(1,100):        # this will go 1, 2, ... , 99
    q = random.randint(0, 99) # q is a random number 0-99
    w = random.randint(0, 99) # w is a random number 0-99
    e = q * w                 # e is q times w
    q = []                    # q is now an empty list
    print '%s * %s = %s' % (q,w,e)
                              # q is an empty list, so this is wrong

Obviously you're not trying to assign q to an empty list each time. You need to make a list BEFORE the loop, then keep adding to it.

some_list = []                # some_list is an empty list
for _ in range(99):           # this will go 0, 1, ... , 98
    q = random.randint(0, 99) # q is a random number 0-99
    w = random.randint(0, 99) # w is a random number 0-99
    e = q * w                 # e is q times w
    some_list.append(e)       # add e to the list!
    print "%s * %s = %s" % (q,w,e)
                              # print "q * w = e"

Note that when you get a bit more advanced, you can wrap this up nicely as a list comprehension so you don't have to initialize it empty then add to it.

some_list = [random.randint(0,99) * random.randint(0,99) for _ in range(99)]
# equivalent to your code

But this is still a bit past your comfort level. One step at a time! :)

Things to note here that I changed:

• range is a half-open range, eg range(1,100) is 99 numbers, 1-99 . It does not include 100.
• You don't actually USE any of the numbers in your range, you just want to run your loop that many times. The common idiom for this is for _ in range(some_number) . You use an underscore ( _ ) to represent to other coders that you don't use the variable here (note that _ does not represent anything special to Python, it's just convention)
• for _ in range(N) is a quick way to do something N times.
• list.append adds to a list =)

Answer 3

A few notes on style:

1. don't define a list inside a for loop, q=[] in this case, if you want it to store values acrovss the several iterations of the for loop.
2. don't use the same name to define multiple objects inside a loop, q in this case being used both for storing a random number and as a list.

Ways to adding to list:

1. Use append() function of the list object to append a value to the list
2. Overload + operator to concatenate a new value to the original list

So, here's how i would change your code:

1. First define the list outside the loop:

    import random e = []

2. Inside the for loop, use append() function to add value to the master list, e :

    for x in range(0,100): q=random.randint(0,99) w=random.randint(0,99) e_val=q*w # new local variable that resets at each iteration of the loop e.append(e_val) print '%s * %s = %s'%(q,w,e_val)

3. Alternatively, you could have replaced the line e.append(e_val) with the following:

    e += [e_val]