如何从for循环返回每个值

Question

(Using python 3.3.2) Hi, I'm trying to make a crawling function for a text cloud, which would go into a list of links and ideally return a list of the function's output for each element in that list. However, I'm stuck using a print function, print(b), instead of actually returning what I want. In my for loop, how would I return everything I would get from my print(b) statement. It can all be in one list or compiled some way or another. Thank you :) tl;dr: how do I return all the stuff I get from a for loop

def crawl():
    linkList = inputFunction()[1:][0] #makes a list of a bunch of URL's
    for i in range(len(linkList)):
        print(i)
        t = getHTML(linkList[i]) #getHTML returns tuple of text in the input URL
        alreadyCrawl = alreadyCrawl + list(linkList[i]) #ignore this
        t = list(t)
        b = counting(t) #makes dictionary of word counts
        print(b) 
    return

Answer 1

Either you put them in a list and return the list at the end, or you "yield" them (hence creating a generator).

First way:

def f():
    acc = []
    for x in range(10):
        acc.append(someFunctionOfX(x))
    return acc

Second way:

def g():
    for x in range(10):
       yield someFunctionOfX(x)

Maybe the most important difference is the following: If any call to someFunctionOfX causes an exception in example 1, the function won't return anything. In example 2 if let's say the 5th value cannot be yielded for some reason, the previous four have already been yielded and probably used in the caller's context.

Here you can see the difference:

def f():
    acc = []
    for x in range(-3, 4):
        acc.append (2 / x)
    return acc

def g():
    for x in range(-3, 4):
        yield 2 / x

def testF():
    for x in f(): print(x)

def testG():
    for x in g(): print(x)

Calling testF simply fails (ZeroDivisionError: division by zero) and doesn't print anything. Calling testG prints

-0.6666666666666666
-1.0
-2.0

and fails then (ZeroDivisionError: division by zero).

---

My (very personal) criterion for either returning a list or yielding values is the following: If I need the data stored somewhere, I return a list. If I just need to process each member, I yield them.

Answer 2

You can return list of values that you want.

def crawl():
    list_ret = []   #create empty list to store values

    for i in range(len(linkList)):
        # do some stuff
        b = counting(t) #makes dictionary of word counts
        list_ret.append(b)  #append value to list
        print(b) 
    return list_ret   #return list of values

Answer 3

def crawl():
    linkList = inputFunction()[1:][0] #makes a list of a bunch of URL's
    return_list = []
    for i in range(len(linkList)):
        print(i)
        t = getHTML(linkList[i]) #getHTML returns tuple of text in the input URL
        alreadyCrawl = alreadyCrawl + list(linkList[i]) #ignore this
        t = list(t)
        b = counting(t) #makes dictionary of word counts
        return_list.append(b) 
    return return_list